Metal fine-particle composite and method for fabricating the same

ABSTRACT

A nano-composite  10  is described, including a matrix resin  1 , metal fine-particles  3  immobilized in the matrix resin  1 , a binding species  7  immobilized on a part or all of the metal fine-particles  3 , and metal fine-particles  9  indirectly immobilized on the metal fine-particles  3  via the binding species  7 . Each of at least a part of the metal fine-particles  3  has a portion embedded in the matrix resin  1 , and a portion (exposed portion  3   a ) exposed outside of the matrix resin  1 , while the binding species  7  is immobilized on the exposed portions.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of and claims thepriority benefit of U.S. patent application Ser. No. 13/700,132, filedon Nov. 27, 2012, now pending, which is a 372 application of theinternational PCT application serial no. PCT/JP2011/061634, filed on May20, 2011, which claims the priority benefit of Japan application no.2010-123225, filed on May 28, 2010. The entirety of each of theabove-mentioned patent applications is hereby incorporated by referenceherein and made a part of this specification.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to a metal fine-particle composite that can beutilized in, for example, various devices utilizing local surfaceplasmon resonance, and to a method for fabricating the same.

2. Description of Related Art

Local surface plasmon resonance (LSPR) is a phenomenon that theelectrons in metal fine-particles or metal fine-structures having a sizeof several to 100 nanometers interact and resonate with light of aspecific wavelength. From ancient periods, LSPR has been utilized instained glass that shows vivid colors by mixing metal fine-particlesinto glass. Recently, LSPR was studied for applications such asdevelopment of high-output light-emitting laser that utilizes alight-intensity enhancing effect, or bio-sensors that utilize theproperty that the resonance state is changed by molecular binding, etc.

In order to apply the LSPR of such metal fine-particles to sensors andso on, it is necessary to stably immobilize the metal fine-particles ina matrix of a synthetic resin or the like. However, when the metalfine-particles have a nanometer size, the aggregation/dispersionproperty thereof changes. For example, dispersion stabilization due toelectrostatic repulsion is difficult to achieve so that aggregationoccurs easily. Hence, for plasmonic devices utilizing LSPR, how todisperse the metal fine-particles in the matrix in a uniform state is animportant issue.

Conventionally, a sensor utilizing plasmon resonance applies the highlysensitive response of the metal plasmon to the refractive index changeof the interfacial material, wherein a ligand molecule having a specificinteraction with a to-be-detected molecule (analyte) is immobilized bychemical or physical means on the surface of a metal film or metalfine-particles of gold or silver, etc., and the concentration of theanalyte is measured. For a SPR sensor utilizing surface plasmonresonance, the technique of applying a metal film formed throughsputtering or vacuum evaporation as disclosed in Patent Document 1 hasbeen known.

However, because the technique of Patent Document 1 uses a metal film,in a sensor utilizing surface plasmon resonance, an optical equipmentsuch as a prism or a goniometer, etc., is required as an assist forhigh-precision sensing. Hence, there is a drawback that miniaturizingthe measurement apparatus is difficult or the measurement apparatus isnot suitable for simple sensing.

PRIOR-ART DOCUMENTS Patent Documents

-   Patent Document 1: Japanese Patent Publication No. 2006-234472

Non-Patent Documents

-   Non-Patent Document 1: Grabar, K. C. et al., Anal. Chem. 1995, 67,    735-743-   Non-Patent Document 2: Freeman, R. G. et al, Science 1995, 267,    1629-1632

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

When a metal fine-particle composite with metal fine-particles dispersedin a matrix is utilized in applications such as LSPR-based sensors, itis important to have a large absorption spectral intensity at least.Moreover, in general, when the absorption spectrum is sharper, ahigh-sensitivity detection is more possible.

This invention is devised in view of the above problems, and has anobject of providing a metal fine-particle composite having ahigh-intensity and sharp absorption spectrum of the LSPR.

Means for Solving the Problems

After diligent studying of the above facts, the Inventors discoveredthat a metal fine-particle composite having first metal fine-particlesimmobilized in a matrix resin and second metal fine-particles indirectlyimmobilized on the first metal fine-particles can meet the aboverequirements. This invention was accomplished based on the discovery.

Specifically, the metal fine-particle composite of this inventionincludes a matrix resin and metal fine-particles immobilized to thematrix resin, and is characterized in that

a) the metal fine-particles include a plurality of first metalfine-particles immobilized in the matrix resin, and second metalfine-particles indirectly immobilized on the first metal fine-particles,

b) the first metal fine-particles are present independently withoutcontacting with each other, and

c) each of at least a part of the first metal fine-particles has aportion embedded in the matrix resin and a portion exposed outside ofthe matrix resin, while the second metal fine-particles are immobilizedvia a binding species immobilized on the exposed portions.

In the metal fine-particle composite of this invention, the first metalfine-particles may have a particle diameter in the range of 1 nm to 50nm and a mean particle diameter greater than or equal to 3 nm, and thesecond metal fine-particles may have a mean particle diameter in therange of 40 nm to 200 nm.

Moreover, in the metal fine-particle composite of this invention, thefirst metal fine-particles may be present with a distance greater thanor equal to the particle diameter of the larger one of two neighboringfirst metal fine-particles.

Moreover, in the metal fine-particle composite of this invention,another binding species having a functional group interacting with aspecific substance may be immobilized on the surfaces of the secondmetal fine-particles.

Moreover, in the metal fine-particle composite of this invention, thesecond metal fine-particles may be formed from a metal colloidal.

The method for producing a metal fine-particle composite of thisinvention includes:

A) a step of contacting the first metal fine-particles, each of whichhas a portion embedded in the matrix resin and a portion exposed outsideof the matrix resin, with a treating liquid containing the bindingspecies at a temperature of 20° C. or lower to selectively bind thebinding species to the exposed portions; and

B) a step of immobilizing the second metal fine-particles via the abovebinding species having been immobilized.

The method for producing a metal fine-particle composite of thisinvention may further include, before the step A,

C) a step of forming a resin film containing a metal ion or a metalsalt;

D) a step of thermally reducing the metal ion or the metal salt in theresin film to separate a plurality of first metal fine-particles in thematrix resin and

E) a step of etching the surface of the matrix resin to partially exposethe surface of each of at least a part of the first metalfine-particles.

Moreover, the method for producing a metal fine-particle composite ofthis invention may further include, after the step B,

F) a step of immobilizing, on the surfaces of the second metalfine-particles, another binding species having a functional groupinteracting with a specific substance.

Moreover, in the method for producing a metal fine-particle composite ofthis invention, the step B may use a metal colloidal solution containingthe second metal fine-particles in a form of metal colloidal.

Effects of the Invention

Because the metal fine-particle composite of this invention includesfirst metal fine-particles immobilized in a matrix resin and secondmetal fine-particles indirectly immobilized on the first metalfine-particles via a binding species, the absorption spectrum of LSPRhas a sufficiently large intensity and is sharp, so a high-sensitivitydetection is possible by utilizing the composite in applications ofvarious sensors and so on. Moreover, because the first metalfine-particles are immobilized in the matrix resin, they do not peel offfrom the matrix resin, and are also possible to be suitably applied toarbitrary shapes including curved-surface shapes.

Moreover, when the metal fine-particle composite of this inventionfurther has another binding species immobilized on the second metalfine-particles, it can be applied to certain uses such as the sensorsbased on the interaction of the another binding species and a specificsubstance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a cross-sectional structure of thenano-composite in the thickness direction of the same.

FIG. 2 illustrates the structure of the metal fine-particles.

FIG. 3 illustrates the state of the second binding species (ligand)being bonded to the nano-composite.

FIG. 4 illustrates the state of the analyte being specifically bonded tothe ligand.

FIG. 5 shows an image of the nano-composite film 1 b obtained through asurface observation in Example 1.

FIG. 6 shows an image of the nano-composite film 1 d obtained through asurface observation in Example 1.

FIG. 7 shows a surface-observation image of the nano-composite filmobtained in Reference Example 1.

FIG. 8 shows a surface-observation image of the nano-composite filmobtained in Reference Example 2.

DESCRIPTION OF EMBODIMENTS

The embodiments of this invention will be described in details asfollows in reference of appropriate drawings.

<Metal Fine-Particle Composite>

FIG. 1 schematically illustrates a cross-sectional structure in thethickness direction of a nano-composite in which metal fine-particlesare dispersed (simply referred to as “nano-composite”, hereafter) 10 asthe metal fine-particle composite according to this embodiment. Thenano-composite 10 includes a matrix resin 1, metal fine-particles 3(first metal fine-particles) immobilized in the matrix resin 1, abinding species 7 immobilized on a part or all of the metalfine-particles 3, and metal fine-particles 9 (second metalfine-particles) indirectly immobilized on the metal fine-particles 3 viathe binding species 7. FIG. 2 illustrates, in a magnified view, themetal fine-particles 3 (in the state that the binding species 7 is notbonded). Moreover, in FIG. 2, among two neighboring metal fine-particles3, the particle diameter of the larger metal fine-particle 3 isdesignated as D_(1L) and that of the smaller metal fine-particle 3 asD_(1S). However, when the particle diameters are not to bedistinguished, the particle diameter is simply designated as D₁.

The nano-composite 10 may further have a substrate not shown in thefigures. For example, glass, ceramics, a silicon wafer, semiconductor,paper, metal, metal alloy, metal oxide, a synthetic resin, or anorganic/inorganic composite material, etc., can be used as thesubstrate. The shape of the substrate may suitably be a plate shape, asheet shape, a film shape, a mesh shape, a geometrical pattern shape, aconcave-convex shape, a fibrous shape, a bellow shape, a multi-layershape, or a spherical shape, etc. Moreover, the substrates with surfaceshaving been subjected to, for example, a silane coupling agenttreatment, a chemical etching treatment, a plasma treatment, an alkalitreatment, an acid treatment, an ozone treatment, a UV-treatment, anelectrical polishing treatment, or a polishing treatment using anabrasive, etc., can also be utilized.

<Matrix Resin>

The matrix resin 1 may be entirely formed in a film shape, or mayalternatively be formed as a part of a resin film.

When the matrix resin 1 is formed as a part of a resin film, thethickness of the resin film is preferably in the range of 3 μm to 100μm, more preferably in the range of 10 μm to 50 μm.

The resin constituting the matrix resin 1 preferably has a lighttransparency allowing generation of LSPR of the metal fine-particles 3,and, in particular, preferably includes a material transparent to lightwith a wavelength greater than or equal to 380 nm. Such matrix resin 1allows the LSPR to be measured in a light transmission system. On theother hand, a resin almost without a light transparency can also besuitably used as the matrix resin 1, which allows the LSPR to bemeasured in a light reflection system. Such conformations are notlimited to be utilized in light transmission systems and lightreflection systems, and may be utilized as sensitivity sensors thatsense the change of the circumstance of the matrix resin 1.

The resin materials that may be used as the matrix resin 1 are notparticularly limited. Examples thereof include polyimide resins,polyamic acid resins, cardo resins (fluorene resins), polysiloxaneresins such as PDMS (polydimethylsiloxane), polyethylene terephthalateresins, polyphenylene ether resins, epoxy resins, fluorine resins, vinylresins and phenol resins, etc., ion-exchange resins, and so on. Amongthe resins, those having a functional group that interacts with a metalion to form a complex with the metal ion and adsorbs the metal ion ispreferred, as being able to adsorb the metal ion in a state of uniformdispersion. Examples of such functional groups include carboxyl group,sulfonic acid group, quarternary ammonium groups, primary and secondaryamino groups, and phenolic hydroxyl groups, etc. In view of this, forexample, polyamic acid resins and ion-exchange resins, etc. arepreferred. Moreover, in view of being suitable for the thermal treatmentin the separation process of the metal fine-particles 3, the resinpreferably has a thermal resistance at a temperature of at least 140° C.In view of this, using the polyimide resin as the material of the matrixresin 1 is particularly preferred because the polyamic acid resin as itsprecursor has carboxyl groups capable of forming complexes with metalions so that it can adsorbs metal ions in the precursor stage, and alsobecause it has thermal resistance to the thermal treatment. Details ofthe polyimide resin and the polyamic acid resin are described later.Moreover, the above resin material may consist of a single resin, or mayalternatively be used as a mixture of a plurality of resins.

<First Metal Fine-Particles>

The material of the metal fine-particles 3 as the first metalfine-particles is not particularly limited. For example, a metal speciessuch as gold (Au), silver (Ag), copper (Cu), cobalt (Co), nickel (Ni),palladium (Pd), platinum (Pt), tin (Sn), rhodium (Rh) or iridium (Ir),etc., can be used. Moreover, the alloys of these metal species, such asa Pt—Co alloy, can also be used. Among these materials, silver (Au) orsilver (Ag) is particularly preferred.

The metal fine-particles 3 may have various shapes, such as a sphericalshape, an ellipsoid shape, a cubic shape, a truncated tetrahedral shape,a bipyramid shape, a regular octahedral shape, a regular decahedralshape, and a regular icosahedral shape, etc. However, in order toinhibit aggregation of the metal fine-particles 9 being the second metalfine-particles and indirectly immobilize the metal fine-particles 9 in anearly uniform state, the spherical shape is more preferred. Herein, theshape of the metal fine-particles 3 can be identified using atransmission electron microscope (TEM). The spherical metalfine-particles 3 are defined as metal fine-particles having a sphericalshape or a nearly spherical shape, wherein the ratio of the average longdiameter to the average short diameter is 1 or close to 1 (greater thanor equal to 0.8 is preferred). Moreover, regarding the relationshipbetween the long diameter and the short diameter of any individual metalfine-particle 3, it is preferred that the long diameter is less than1.35 times the short diameter, and is more preferred that the longdiameter is equal to or less than 1.25 times the short diameter.Moreover, when the metal fine-particles 3 do not have a spherical shapebut have, for example, a regular octahedral shape, the largest one amongthe edge lengths of a metal fine-particle 3 is taken as the longdiameter of the same, the smallest one among the edge lengths is takenas the short diameter of the same, and the above long diameter isconsidered as the particle diameter D₁ of the same.

The metal fine-particles 3 are present independently without contactingwith each other, and in particular, are preferably present with adistance greater than or equal to the particle diameter of the largerone of two neighboring metal fine-particles. For example, the distance(inter-particle distance) L₁ between two neighboring metalfine-particles 3 is preferably greater than or equal to the particlediameter D_(1L) of the larger one of the neighboring metalfine-particles 3 (L₁≧D_(1L)). In cases where the distance is in theabove range, when the metal fine-particles 9, which are the second metalfine-particles, are being immobilized, it is easy to inhibit aggregationof the metal fine-particles 9 with each other. On the other hand, thoughthe inter-particle distance L₁ can be made large without causingparticular problems, its upper limit is preferably controlled based onthe lower limit of the volume fraction of the metal fine-particles 3,because the inter-particle distance L₁ of the metal fine-particles 3that are made into a dispersion state possibly through thermal diffusionis closely correlated to the particle diameter D₁ and the volumefraction of the metal fine-particles 3. When the inter-particle distanceL₁ is large, i.e., when the volume fraction of the metal fine-particles3 in the nano-composite 10 is less, the number of the metalfine-particles 9 immobilized on the metal fine-particles 3 is decreased,so that the intensity of the absorption spectrum of the LSPR from themetal fine-particles 9 is low. In such cases, for example, it ispreferred that the mean particle diameter of the metal fine-particles 9as described later is greater than or equal to 80 nm.

For at least a part of the metal fine-particles 3, each of them has aportion embedded in the matrix resin 1 and a portion (exposed portion 3a) exposed outside of the matrix resin 1, while a binding species 7 isimmobilized on the exposed portions. Because the metal fine-particle 3has a portion embedded in the matrix resin 1, it can be immobilizedfirmly in the matrix resin 1 by the anchoring effect. Moreover, becausethe metal fine-particles 3 have the exposed portions 3 a, the bindingspecies can be immobilized thereon. Accordingly, it is preferred thatfor all of the metal fine-particles 3 immobilized in the matrix resin 1,each has an exposed portion 3 a and has a binding species 7 immobilizedon the exposed surface 3 a. However, it is feasible that there are metalfine-particles 3 entirely embedded in the matrix resin 1 and have nobinding species 7 immobilized thereon. The proportion of the metalfine-particles 3 having exposed portions 3 a is set, for example, interms of the ratio of the total area of the exposed portions 3 a to thesurface area of the matrix resin 1 (including the surface area of theexposed portions 3 a), preferably in the range of 0.1% to 18% and morepreferably in the range of 0.2% to 10%. Moreover, the surface area ofthe exposed portion 3 a of a metal fine-particle 3 can be calculatedfrom the two-dimensional image obtained from an observation using, forexample, a field-emitting scanning electron microscope (FE-SEM).Moreover, because the ratio of the total area of the exposed portions 3a to the surface area of the matrix resin 1 is closely correlated to thevolume fraction of the metal fine-particles 3, the volume fraction ofthe metal fine-particles 3 is preferably controlled to be in thepreferred range described later.

The metal fine-particles 3 are dispersed into a layer having a certainthickness, in the surface direction parallel with the surface S of thematrix resin 1 (the surface of he nano-composite 10), to form a metalfine-particle layer 5. Though the thickness T of the metal fine-particlelayer 5 varies with the particle diameter D₁ of the metal fine-particles3, in the applications utilizing LSPR, the thickness T of the metalfine-particle layer 5 is preferably in the range of 20 nm to 25 μm, andmore preferably in the range of 30 nm to 1 μm. Herein, “the thickness Tof the metal fine-particle layer 5” means, in a cross section in thethickness direction of the matrix resin 1, the thickness from the topend of the most upward positioned metal fine-particle 3 (but whichshould be one having a particle diameter in the range of 1 nm to 50 nm)at the side of exposure from the matrix resin 1 to the bottom end of themost downward (deeply) positioned metal fine-particle 3 (but whichshould be one having a particle diameter in the range of 1 nm to 50 nm).

Moreover, in the application of detecting the change of the circumstanceof the matrix resin 1, the metal fine-particles 3 entirely embedded inthe matrix are almost uncorrelated to the change of the circumstance. Inview of this, the thickness T of the metal fine-particle layer 5constituted by the metal fine-particles 3 is more preferably in therange of 10 nm to 80 nm.

Moreover, when the cross section parallel with the surface S of thematrix resin 1 is observed, it is the most preferred mode of thenano-composite 10 that all the metal fine-particles 3 are completelyindependent from each other. In such a case, the thickness T′ of themetal fine-particle layer 5 constituted only by metal fine-particles 3having exposed portions 3 a is preferably in the range of 20 nm to 40nm, for example. Moreover, the particle diameter D₁ of the metalfine-particles 3 is preferably in the range of 10 nm to 30 nm. Bysetting the values in the ranges, the intensity of the absorptionspectrum of the LSPR from the metal fine-particles 3 can be inhibited tobe low. Herein, “the thickness T′ of the metal fine-particle layer 5”means, in a cross section in the thickness direction of the matrix resin1, the thickness from the top end of the most upward positioned one (butwhich should be one having a particle diameter in the range of 10 nm to30 nm) of the metal fine-particles 3 having exposed portions 3 a at theside of exposure of the matrix resin 1 to the bottom end of the mostdownward (deeply) positioned one (but which should be one having aparticle diameter in the range of 10 nm to 30 nm) of the metalfine-particles 3 having exposed portions 3 a.

Moreover, by making the particle diameter D₁ of the metal fine-particles3 present in the matrix resin 1 be greater than or equal to 10 nm, withthe metal fine-particles 3 dottedly distributed in a single layer, therelatively larger metal fine particles 9 having a higher intensity ofabsorption spectrum and a mean particle diameter about 100 nm can beimmobilized in a large number without aggregation, so that a detectionof higher sensitivity is possible. Herein, that the metal fine-particles3 are dottedly distributed in a single layer means that they aredistributed about two-dimensionally inside of the matrix resin 1. Inother words, it is preferred that 90% or more of the total metalfine-particles 3 are dispersed, within the depth of 40 nm from thesurface S of the matrix resin, in the plane direction parallel to thesurface S to form a metal fine-particle layer 5, and only one metalfine-particle 3 having a particle diameter D₁ in the range of 10 nm to30 nm is present in the depth direction in the metal fine-particle layer5. That is, though not shown in the figures, when the cross section ofthe nano-composite 10 parallel to the surface S of the matrix resin 1 isobserved, in the interior (or the surface S) of the matrix resin 1, aplurality of metal fine-particles 3 having particle diameters D₁ in therange of 10 nm to 30 nm are observed to be dottedly distributed anddiffuse with an inter-particle distance L₁. Meanwhile, when a crosssection along the depth direction of the matrix resin 1 is observed, asshown in FIG. 1, a plurality of metal fine-particles 3 having a particlediameter D₁ in the range of 10 nm to 30 nm are completely independentlyand dottedly distributed into a single layer (substantially in a row,though with a certain positional variation) in the ambit of the metalfine-particle layer 5. Moreover, the method of observing the crosssection parallel to the surface S of the matrix resin 1 may be, forexample, using a scanning electron microscope (SEM) given a sputteringfunction to sputter and observe the surface layer of the matrix resin 1.

The existence proportion of the metal fine-particles 3 with particlediameter D₁ of from 1 nm to less than 10 nm, which may be measured byobserving a cross-section of the matrix resin 1 using a transmissionelectron microscope (TEM), is preferably less than 50%, more preferablyless than 10% and even more preferably less than 1%, relative to thetotal metal fine-particles 3 in the nano-composite 10. Herein, the“existence proportion” is calculated by dividing the sum of thecross-sectional areas of the metal fine-particles 3 with particlediameters D₁ of from 1 nm to less than 10 nm by the sum of thecross-sectional areas of all the metal fine-particles 3. Herein, whenmetal fine-particles 3 with particle diameters D₁ less than 10 nm arepresent, apparent overlapping of metal fine-particles 3 is identified inthe thickness direction of the nano-composite 10. In such a case,relative to the sum of the cross-sectional areas of all the metalfine-particles 3 being observed, the ratio of the sum of thecross-sectional areas of the metal fine-particles 3 observed to beentirely independent from each other is preferably 90% or more, morepreferably 95% or more, and even more preferably 99% or more. Moreover,because it is easier to control the surface areas of the exposedportions 3 a to be uniform when the particle-diameter distribution ofthe metal fine-particles 3 is narrower, it is preferred to control theparticle-diameter distribution of the metal fine-particles 3 to benarrow. In view of this, about the particle-diameter distribution of themetal fine-particles 3, it is preferred that the maximal particlediameter (D_(1max)) and the minimal particle diameter (D_(1min)) satisfythe relationship of “(⅓×D_(1max))<(1×D_(1min))”. Moreover, since theparticle diameter D₁ of the metal fine-particles 3 is closely correlatedto the thickness (T′) of the metal fine-particle layer 5, it ispreferred that the thickness T′ (nm) of the metal fine-particle layer 5and the maximal particle diameter D_(1max) satisfy“(½×T′)<(1×D_(1max))”.

Moreover, it is also feasible that the metal fine-particles 3 aredispersed three-dimensionally inside of the matrix resin 1. That is,when a cross section of the nano-composite 10 along the thicknessdirection of the film-shaped matrix resin 1 is observed, as shown inFIG. 1, a plurality of metal fine-particles 3 are dottedly distributedin the longitudinal direction and in the transverse direction with aninter-particle distance L₁ greater than or equal to the above particlediameter D_(1L). Meanwhile, when the cross section of the nano-composite10 parallel with the surface of the matrix resin 1 is observed, thoughnot shown in the figures, a plurality of metal fine-particles 3 isdottedly distributed and diffuses inside of the matrix resin 1 with aninter-particle distance L₁ greater than or equal to the above particlediameter D_(1L).

Moreover, it is preferred that 90% or more of the metal fine-particles 3are single particles dottedly distributed in the matrix resin 1 with aninter-particle distance L₁ greater than or equal to the above particlediameter D_(1L). Herein, the term “single particles” means that themetal fine-particles 3 are independently present in the matrix resin 1but do not include aggregations of multiple particles (aggregatedparticles). That is, the single particles do not include aggregatedparticles formed by aggregation of multiple metal fine-particles throughan inter-molecular force. Moreover, an “aggregated particle” can beclearly identified by, for example, an observation using a transmissionelectron microscope (TEM), to be one aggregate formed by an assembly ofmultiple individual metal fine-particles. Moreover, though in terms ofits chemical structure, the metal fine-particles 3 in the nano-composite10 are known to be metal fine-particles formed by aggregation of metalatoms formed by thermal reduction, they are considered to be formed bymetal bonding of metal atoms and be different from the aggregatedparticles formed by aggregation of multiple particles. For example, whena transmission electron microscope (TEM) is used to observe, a singleindependent metal fine-particle 3 can be identified. By making the abovesingle particles present in a proportion of 90% or more and preferably95% or more, the metal fine-particles 9 can be indirectly immobilizeduniformly, so that the absorption spectrum of LSPR is sharp and stable,and a high detection sensitivity is obtained. This means, in otherwords, that the proportion of the aggregated particles or the particlesdispersed with an inter-particle distance L₁ less than the aboveparticle diameter D_(1L) is less than 10%. Moreover, when the proportionof the aggregated particles or the particles dispersed with aninter-particle distance L₁ less than the above particle diameter D_(1L)exceeds 10%, controlling the particle diameters D₁ is very difficult.

In the nano-composite 10 of this embodiment, the metal fine-particles 3as the first metal fine-particles preferably further meet the followingrequirements i) to ii).

i) The metal fine-particles 3 are preferably obtained by reducing themetal ion or a metal salt contained in the matrix resin 1 or itsprecursor resin. The reduction method may be light reduction or thermalreduction, etc.; but in view of controlling the particle distance of themetal fine-particles 3, the products obtained by thermal reduction arepreferred. Specific contents of the reduction method are describedlater.

ii) The particle diameter (D₁) of the metal fine-particles 3 may be inthe range of 1 nm to 50 nm, and is preferably in the range of 3 nm to 30nm. The mean particle diameter D_(1A) is preferably greater than orequal to 3 nm. The mean particle diameter D_(1A) of the metalfine-particles 3 means the area mean diameter obtained by measuring 100arbitrary metal fine-particles 3. If the particle diameter (D₁) of themetal fine-particles 3 exceeds 50 nm, the number of the metalfine-particles 9 immobilized on the metal fin-particles 3 is decreased,and a sufficient LSPR effect of the metal fine-particles 9 is difficultto obtain. Moreover, in order to distribute the metal fin-particles 3 ina single layer to thereby improve the sensitivity, it is more preferredthat the particle diameters D₁ of 90% to 100% of the total metalfine-particles 3 are in the range of 10 nm to 30 nm.

When the metal fine-particles 3 are not spherical, the larger theirapparent diameter is, the more easily the indirectly immobilized metalfine-particles 9 aggregate. Hence, when the metal fine-particles 3 arenot spherical, the particle diameter D₁ is preferably 30 nm or less,more preferably 20 nm or less and even more preferably 10 nm or less.Moreover, in cases where the metal fine-particles 3 are not spherical,while respective metal fine-particles 3 present in the matrix resin 1are compared with each other for the shape, it is preferred that 80% ormore, and more preferably 90% or more, of the total metal fine-particles3 have substantially the same shape, especially in a relative manner.

It is also feasible that metal fine-particles 3 having particlediameters D₁ less than 1 nm are present in the nano-composite 10. Such anano-composite 10 hardly affects the LSPR and hence has no particularproblems. Moreover, the amount of the metal fine-particles 3 havingparticle diameters D₁ less than 1 nm, for example in a case where themetal fine-particles 3 are silver fine-particles, is preferably 10 partsby weight or less and more preferably 1 part by weight or less, relativeto 100 parts by weight of the total metal fine-particles 3 in thenano-composite 10. Herein, the metal fine-particles 3 having particlediameters D₁ less than 1 nm can be observed using, for example, ahigh-resolution transmission electron microscope.

Moreover, to inhibit aggregation of the metal fine-particles 9 as thesecond metal fine-particles and indirectly immobilize the same in anearly uniform state, the mean particle diameter D_(1A) of the metalfine-particles 3 is suitably greater than or equal to 3 nm, preferablybetween 3 nm and 30 nm, and more preferably between 3 nm and 20 nm.

Moreover, the volume fraction of the metal fine-particles 3 in thematrix resin 1 relative to the nano-composite 10 is preferably 0.1% to23% and more preferably 0.3% to 12%. Herein, the “volume fraction” is avalue indicating the percentage of the total volume of the metalfine-particles 3 in a certain volume of the nano-composite 10. If thevolume fraction of the metal fine-particles 3 is less than 0.1%, theeffect of this invention is difficult to obtain. On the contrary, if thevolume fraction exceeds 23%, the distance (inter-particle distance L₁)between two neighboring metal fine-particles 3 is less than the particlediameter D_(1L) of the larger one of two neighboring metalfine-particles 3, so that it is difficult to control the immobilizationof the metal fine-particles 9, which are the second metalfine-particles, to be uniform.

<Binding Species>

The binding species 7 in the nano-composite 10 of this embodiment can bedefined as, for example, a substance that has a functional group X1capable of bonding with the metal fine-particles 3 and a functionalgroup Y1 interacting with the metal fine-particles 9. The bindingspecies 7 is not limited to a single molecule, and also covers, forexample, a composite constituted of two or more components, etc. Thebinding species 7 is bonded with the metal fine-particles 3 via thefunctional group X1 and immobilized on the exposed portions 3 a of themetal fine-particles 3. In such a case, the bonding between thefunctional group X1 and the metal fine-particles 3 indicates, forexample, chemical bonding, or physical bonding through adsorption or thelike, etc.

The functional group X1 of the binding species 7 is a functional groupimmobilized on the surfaces of the metal fine-particles 3, which may beimmobilized by chemically bonding to the surfaces of the metalfine-particles, or be immobilized through adsorption. Examples of suchfunctional group X1 include monovalent groups such as —SH, —NH₂, —NH₃X(X is a halogen atom), —COOH, —Si(OCH₃)₃, —Si(OC₂H₅)₃, —SiCl₃ and—SCOCH₃, etc., and divalent groups such as —S₂— and —S₄—, etc. Thepreferred groups among them are those containing one or more sulfuratoms, such as the mercapto group, the sulfide group and the disulfidegroup, etc.

Moreover, the functional group Y1 of the binding species 7 may be, forexample, a substituent capable of bonding with a metal or an inorganiccompound such as a metal oxide. Examples of such interaction-enablingfunctional group Y1 include —SH, —NH₂, —NR₃X (R is a hydrogen atom or aC₁-C₆ alkyl group, and X is a halogen atom), —COOR (R is a hydrogen atomor a C₁-C₆ alkyl group), —Si(OR)₃ (R is a C₁-C₆ alkyl group), SiX₃ (X isa halogen atom), —SCOR (R is a C₁-C₆ alkyl group), —OH, —CONH₂, —N₃,—CR═CHR′ (R and R′ are each independently a hydrogen atom or a C₁-C₆alkyl group), —C≡CR (R is a hydrogen atom or a C₁-C₆ alkyl group),—PO(OH)₂, —COR (R is a C₁-C₆ alkyl group), imidazolyl, andhydroquinolyl, etc.

Specific examples of the binding species 7 include HS—(CH₂)_(n)—OH (n=11or 16), HS—(CH₂)_(n)—COOH (n=10, 11 or 15), HS—(CH₂)_(n)—NH₂.HCl (n=10,11 or 16), HS—(CH₂)₁₁—N(CH₃)₃ ⁺Cl⁻, HS—(CH₂)₁₁—PO(OH)₂,HS—(CH₂)₁₀—CH(OH)—CH₃, HS—(CH₂)₁₀—COCH₃, HS—(CH₂)_(n)—N₃ (n=10, 11, 12,16 or 17), HS—(CH₂)_(n)—CH═CH₂ (n=9 or 15), HS—(CH₂)₄—C≡CH,HS—(CH₂)_(n)—CONH₂ (n=10 or 15), HS—(CH₂)₁₁—(OCH₂CH₂)_(n)—OCH₂—CONH₂(n=3 or 6), HO—(CH₂)₁₁—S—S—(CH₂)₁₁—OH, andCH₃—CO—S—(CH₂)₁₁—(OCH₂CH₂)_(n)—OH (n=3 or 6), etc.

Other examples of the binding species 7 include: heterocyclic compoundshaving an amino group or a mercapto group, such as2-amino-1,3,5-triazine-4,6-dithiol, 3-amino-1,2,4-triazole-5-thiol,2-amino-5-trifluoromethyl-1,3,4-thiadiazole,5-amino-2-mercaptobenzimidazole, 6-amino-2-mercaptobenzothiazole,4-amino-6-mercaptopyrazolo[3,4-d]pyrimidine,2-amino-4-methoxybenzothiazole, 2-amino-4-phenyl-5-tetradecylthiazole,2-amino-5-phenyl-1,3,4-thiadiazole, 2-amino-4-phenylthiazole,4-amino-5-phenyl-4H-1,2,4-triazole-3-thiol,2-amino-6-(methylsulfonyl)benzothiazole, 2-amino-4-methylthiazole,2-amino-5-(methylthio)-1,3,4-thiadiazole,3-amino-5-methylthio-1H-1,2,4-thiazole, 6-amino-1-methyluracil,3-amino-5-nitrobenzisothiazole, 2-amino-1,3,4-thiadiazole,5-amino-1,3,4-thiadiazole-2-thiol, 2-aminothiazole,2-amino-4-thiazoleacetic acid, 2-amino-2-thiazoline,2-amino-6-thiocyanatobenzothiazole, DL-α-amino-2-thiopheneacetic acid,4-amino-6-hydroxy-2-mercaptopyrimidine, 2-amino-6-purinethiol,4-amino-5-(4-pyridyl)-4H-1,2,4-triazole-3-thiol,N⁴-(2-amino-4-pyrimidinyl)sulfanylamide, 3-aminorhodanine,5-amino-3-methylisothiazole, 2-amino-α-(methoxyimino)-4-thiazoleaceticacid, thioguanine, 5-amino-tetrazole, 3-amino-1,2,4-triazine,3-amino-1,2,4-triazole, 4-amino-4H-1,2,4-triazole, 2-aminopurine,aminopyrazine, 3-amino-2-pyrazinecarboxylic acid, 3-aminopyrazole,3-aminopyrazole-4-carbonitrile, 3-amino-4-pyrazolecarboxylic acid,4-aminopyrazolo[3,4-d]pyrimidine, 2-aminopyridine, 3-aminopyridine,4-aminopyridine, 5-amino-2-pyridinecarbonitrile,2-amino-3-pyridinecarboxaldehyde,2-amino-5-(4-pyridinyl)-1,3,4-thiadiazole, 2-aminopyrimidine,4-aminopyrimidine, and 4-amino-5-pyrimidinecarbonitrile, etc; and silanecoupling agents having an amino group or a mercapto group, such as3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane,N-2-(aminoethyl)-3-aminopropyltrimethoxysilane,N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane,3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine,N-phenyl-3-aminopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane,3-mercaptopropyltrimethoxysilane,N-2-(mercaptoethyl)-3-mercaptopropyltrimethoxysilane,N-2-(mercaptoethyl)-3-mercaptopropylmethyldimethoxysilane,3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylmercapto, andN-phenyl-3-mercaptopropyltrimethoxysilane, etc. Moreover, the bindingspecies 7 is not particularly limited to the above compounds, and thebinding species 7 may include the above compounds alone or incombination of two or more thereof.

Moreover, the molecular skeleton of the binding species 7 between thefunctional groups X1 and Y1 includes atoms selected from the groupconsisting of carbon, oxygen and nitrogen atoms, and may have, e.g., astraight or branched chemical structure with a straight moiety ofC₂-C₂₀, preferably C₂-C₁₅ and more preferably C₂-C₁₀, or a cyclicchemical structure. The molecular skeleton may be designed using asingle molecule species, or alternatively using two or more moleculespecies. In an example of suitably applied embodiments where, forexample, a detection object molecule or the like is to be effectivelydetected, it is preferred that the thickness of the molecular mono-film(or molecular monolayer) formed by the binding species 7 is within therange of about 1.3 nm to 3 nm. In view of this, a binding species 7having a C₁₁-C₂₀ alkane chain as a molecular skeleton is preferred. Insuch a case, because the long alkane chain immobilized on the surface ofthe metal fine-particle 3 via the functional group X1 extends verticallyfrom the surface to form a molecular mono-film (molecular monolayer),the functional group Y1 suffuses the surface of the molecular mono-film(molecular monolayer).

Well-known thiol compounds useful as reagents for forming self-assemblymono-films (SAM) can be suitably used as such binding species 7.

<Second Metal Fine-Particles>

The material of the metal fine-particles 9, which are the second metalfine-particles, is not particularly limited, and may be a metal speciessuch as gold (Au), silver (Ag), copper (Cu), cobalt (Co), nickel (Ni),palladium (Pd), platinum (Pt), tin (Sn), rhodium (Rh), or iridium (Ir),etc. Moreover, the alloys of these metal species, such as Pt—Co alloys,can also be used. Among them, gold (Au), silver (Ag), copper (Cu),palladium (Pd), platinum (Pt), tin (Sn), rhodium (Rh) and iridium (Ir)can be suitably uses as LSPR-effecting metal species, while gold (Au)and silver (Ag) are particularly preferred. The metal fine-particles 9may include the same metal species of the metal fine-particles 3, or mayinclude a metal species different from that of the metal fine-particles3. The metal fine-particles 9 are preferably formed from a metalcolloidal containing the above metal, for example. In cases using ametal colloidal, for example in a case using a metal gold colloidal, thesurface of the metal gold colloidal can be covered by a protective groupsuch as citric acid. That is, the surface of the metal goldfine-particles can be covered by citric acid, as described in the aboveNon-Patent Document 1 or 2. When the functional group Y1 of the bindingspecies 7 is, for example, an amino group, it can substitute the citricacid and directly chemically bonds with the metal gold fine-particle.

The metal fine-particles 9 may have various shapes, such as a sphericalshape, an ellipsoid shape, a cubic shape, a truncated tetrahedral shape,a bipyramid shape, a regular octahedral shape, a regular decahedralshape, and a regular icosahedral shape, etc. However, in order tosharpen the absorption spectrum of the LSPR, the spherical shape is morepreferred. Herein, the shape of the metal fine-particles 9 can beidentified using a transmission electron microscope (TEM). The sphericalmetal fine-particles 9 are defined as metal fine-particles having aspherical shape or a nearly spherical shape, wherein the ratio of theaverage long diameter to the average short diameter is 1 or close to 1(greater than or equal to 0.8 is preferred). Moreover, about therelationship between the long diameter and the short diameter of anyindividual metal fine-particle 3, it is preferred that the long diameteris less than 1.35 times the short diameter, and is more preferred thatthe long diameter is equal to or less than 1.25 times the shortdiameter. Moreover, when the metal fine-particles 9 do not have aspherical shape but have, for example, a regular octahedral shape, thelargest one among the edge lengths of a metal fine-particle 9 is takenas the long diameter of the same, the smallest one among the edgelengths is taken as the short diameter of the same, and the above longdiameter is considered as the particle diameter D₂ of the same.

The particle diameter D₂ of the metal fine-particles 9 is preferably inthe range of 30 nm to 250 nm and more preferably in the range of 50 nmto 200 nm. If the particle diameter D₂ of the metal fine-particles 9exceeds 250 nm, the amount (or the number) of the adhering metalfine-particles 9 is decreased, and a sufficient LSPR effect is notobtained. If the particle diameter D₂ of the metal fine-particles 9 isless than 30 nm, the function of enhancing the LSPR effect is notobtained. Moreover, the mean particle diameter D_(2A) of the metalfine-particles 9 is preferably in the range of 40 nm to 200 nm and morepreferably in the range of 80 nm to 150 nm. Herein, the mean particlediameter D_(2A) of the metal fine-particles 9 means the area-averageddiameter obtained by measuring 100 arbitrary metal fine-particles 9.Moreover, it is more preferred that the particle diameters D₂ of 90% to100% of the total metal fine-particles 9 are in the range of 30 nm to200 nm.

As shown in FIG. 3, for example, a second binding species (bindingspecies 11) different from the binding species 7 as the first bindingspecies can be immobilized on the surfaces of the metal fine-particles9. In the nano-composite 10 of this embodiment, the binding species 11can be defined as, for example, a substance including a functional groupX2 capable of binding with the metal fine-particles 9 and a functionalgroup Y2 interacting with a specific substance such as adetection-object molecule or the like. The binding species 11 is notlimited to a single molecule, and also covers, for example, a compositeconstituted of two or more components. The binding species 11 isimmobilized on the surfaces of the metal fine-particles 9 via thebonding between the functional group X2 and the metal fine-particles 9.Herein, the bonding between the functional group X2 and the metalfine-particles 9 means a chemical bonding, or a physical bonding such asadsorption and so on. Moreover, the interaction between the functionalgroup Y2 and the specific substance means, for example, a chemicalbonding, or a physical bonding such as adsorption and so on, and mayalternatively mean that the functional group Y2 is partially or entirelyaltered (modified or removed, etc.), and so on.

The functional group X2 of the binding species 11 is for immobilizingthe binding species 11 on the surfaces of the metal fine-particles 9,and may be immobilized on the surfaces of the metal fine-particles 9through chemical bonding, or alternatively be immobilized throughadsorption. Examples of such functional group X2 include the samedivalent groups among the above examples of the functional group X1 ofthe binding species 7, wherein those containing one or more sulfuratoms, such as the mercapto group, the sulfide group and the disulfidegroup, etc., are preferred.

Moreover, the functional group Y2 of the binding species 11 may be, forexample, a substituent capable of bonding with a metal, an inorganiccompound such as a metal oxide, or an organic compound such as DNA orprotein, or alternatively, a leaving group that may leave due to, forexample, an acid or an alkali, etc. Examples of the functional group Y2allowing such interaction include, in addition to those in the examplesof the functional group Y1 of the binding species 7, —SO₃ ⁻X (X is analkali metal), N-hydroxysuccinimide group (—NHS), a Biotin group,—SO₂CH₂CH₂X (X is a halogen atom, —OSO₂CH₃, —OSO₂C₆H₄CH₃, —OCOCH₃, —SO₃⁻, or pyridium), etc.

Specific examples of the binding species 11 include: HS—(CH₂)_(n)—OH(n=1 or 16), HS—(CH₂)_(n)—COOH (n=10, 11 or 15), HS—(CH₂)_(n)—COO—NHS(n=10, 11 or 15), HS—(CH₂)_(n)—NH₂.HCl (n=10, 11 or 16),HS—(CH₂)₁₁—NHCO-Biotin, HS—(CH₂)₁₁—N(CH₃)₃ ⁺Cl⁻, HS—(CH₂)_(n)—SO₃ ⁻Na⁺(n=10, 11, or 16), HS—(CH₂)₁₁—PO(OH)₂, HS—(CH₂)₁₀—CH(OH)—CH₃,HS—(CH₂)₁₀—COCH₃, HS—(CH₂)_(n)—N₃ (n=10, 11, 12, 16 or 17),HS—(CH₂)_(n)—CH═CH₂ (n=9 or 15), HS—(CH₂)₄—C≡CH, HS—(CH₂)_(n)—CONH₂(n=10 or 15), HS—(CH₂)₁₁—(OCH₂CH₂)_(n)—OCH₂—CONH₂ (n=3 or 6),HO—(CH₂)₁₁—S—S—(CH₂)₁₁—OH, and CH₃—CO—S—(CH₂)₁₁—(OCH₂CH₂)_(n)—OH (n=3 or6).

Other examples of the binding species 11 include: heterocyclic compoundshaving an amino group or a mercapto group, such as2-amino-1,3,5-triazine-4,6-dithiol, 3-amino-1,2,4-triazole-5-thiol,2-amino-5-trifluoromethyl-1,3,4-thiadiazole,5-amino-2-mercaptobenzimidazole, 6-amino-2-mercaptobenzothiazole,4-amino-6-mercaptopyrazolo[3,4-d]pyrimidine,2-amino-4-methoxybenzothiazole, 2-amino-4-phenyl-5-tetradecylthiazole,2-amino-5-phenyl-1,3,4-thiadiazole, 2-amino-4-phenylthiazole,4-amino-5-phenyl-4H-1,2,4-triazole-3-thiol,2-amino-6-(methylsulfonyl)benzothiazole, 2-amino-4-methylthiazole,2-amino-5-(methylthio)-1,3,4-thiadiazole,3-amino-5-methylthio-1H-1,2,4-thiazole, 6-amino-1-methyluracil,3-amino-5-nitrobenzisothiazole, 2-amino-1,3,4-thiadiazole,5-amino-1,3,4-thiadiazole-2-thiol, 2-aminothiazole,2-amino-4-thiazoleacetic acid, 2-amino-2-thiazoline,2-amino-6-thiocyanatobenzothiazole, DL-α-amino-2-thiopheneacetic acid,4-amino-6-hydroxy-2-mercaptopyrimidine, 2-amino-6-purinethiol,4-amino-5-(4-pyridyl)-4H-1,2,4-triazole-3-thiol,N⁴-(2-amino-4-pyrimidinyl)sulfanylamide, 3-aminorhodanine,5-amino-3-methylisothiazole, 2-amino-α-(methoxyimino)-4-thiazoleaceticacid, thioguanine, 5-amino-tetrazole, 3-amino-1,2,4-triazine,3-amino-1,2,4-triazole, 4-amino-4H-1,2,4-triazole, 2-aminopurine,aminopyrazine, 3-amino-2-pyrazinecarboxylic acid, 3-aminopyrazole,3-aminopyrazole-4-carbonitrile, 3-amino-4-pyrazolecarboxylic acid,4-aminopyrazolo[3,4-d]pyrimidine, 2-aminopyridine, 3-aminopyridine,4-aminopyridine, 5-amino-2-pyridinecarbonitrile,2-amino-3-pyridinecarboxaldehyde,2-amino-5-(4-pyridinyl)-1,3,4-thiadiazole, 2-aminopyrimidine,4-aminopyrimidine, and 4-amino-5-pyrimidinecarbonitrile, etc; and silanecoupling agents having an amino group or a mercapto group, such as3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane,N-2-(aminoethyl)-3-aminopropyltrimethoxysilane,N-2-(aminoethyl)-3-aminopropylmethyldimethoxysilane,3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylamine,N-phenyl-3-aminopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane,3-mercaptopropyltrimethoxysilane,N-2-(mercaptoethyl)-3-mercaptopropyltrimethoxysilane,N-2-(mercaptoethyl)-3-mercaptopropylmethyldimethoxysilane,3-triethoxysilyl-N-(1,3-dimethylbutylidene)propylmercapto, andN-phenyl-3-mercaptopropyltrimethoxysilane, etc. Moreover, the bindingspecies 11 is not particularly limited to the above compounds, and thebinding species 11 may include the above compounds alone or incombination of two or more thereof.

Moreover, the molecular skeleton of the binding species 11 between thefunctional groups X2 and Y2 includes atoms selected from the groupconsisting of carbon, oxygen and nitrogen atoms, and may have, e.g., astraight or branched chemical structure with a straight moiety ofC₂-C₂₀, preferably C₂-C₁₅ and more preferably C₂-C₁₀, or a cyclicchemical structure. The molecular skeleton may be designed using asingle molecule species, or alternatively using two or more moleculespecies. In an example of suitably applied embodiments where, forexample, a detection-object molecule or the like is to be effectivelydetected, it is preferred that the thickness of the molecular mono-film(or molecular monolayer) formed by the binding species 7 is in the rangeof about 1.3 nm to 3 nm. In view of this, a binding species 7 having aC₁₁-C₂₀ alkane chain as a molecular skeleton is preferred. In such acase, for the long alkane chain immobilized on the surface of the metalfine-particle 3 via the functional group X2 extends vertically from thesurface to form a molecular mono-film (molecular monolayer), thefunctional group Y2 suffuses the surface of the molecular mono-film(molecular monolayer). Well-known thiol compounds useful as reagents forforming self-assembly mono-films (SAM) can be suitably used as suchbinding species 11.

Because the nano-composite 10 of this embodiment includes metalfine-particles 3 immobilized in the matrix resin 1, and metalfine-particles 9 immobilized on the dottedly distributed portions of themetal fine-particles 3 exposed outside of the matrix resin 1 via thebinding species 7, the relatively larger metal fine-particles 9 havingan mean particle diameter greater than or equal to 40 nm can be formedin a state of substantially uniformly dispersed in a two-dimensionalmanner in the surface direction of the nano-composite 10. Therefore, ascompared to the nano-composites having the metal fine-particles 3 only,the absorption spectrum of the LSPR is more intense and sharper. In viewof this, with respect to the existence ratio of the metal fine-particles3 having the exposed portions 3 a to the metal fine-particles 9, it ispreferred that the number of the metal fine-particles 3 having theexposed portions 3 a is more than the number of the metal fine-particles9 indirectly immobilized on the metal fine-particles 3 via the bindingspecies 7. In order to obtain a sufficient LSPR effect, the existenceratio of the metal fine-particles 3 having the exposed portions 3 a tothe metal fine-particles 9, which is defined as the ratio of the numberof the metal fine-particles 9 to the number of the metal fine-particles3 having the exposed portions 3 a, is preferably in the range of 0.01 to1.0 and more preferably in the range of 0.02 to 1.0.

Moreover, the relationship between the mean particle diameter D_(1A) ofthe metal fine-particles 3 and the mean particle diameter D_(2A) of themetal fine-particles 9 is not particularly limited, but the relationshipof “D_(1A)<D_(2A)” is preferred. Because the existence ratio of themetal fine-particles 9 to the metal fine-particles 3 gets smaller as themean particle diameter D_(2A) of the metal fine-particles 9 gets larger,in order to obtain a sufficient LSPR effect, the ratio (D_(2A)/D_(1A))of the mean particle diameters D_(1A) and D_(2A) is preferably in therange of 4 to 20 and more preferably in the range of 5 to 15.

In the nano-composite 10 of this embodiment, the metal fine-particles 3and the metal fine-particles 9 interact with light to induce LSPR.However, the absorption peak (referred to as “second peak” hereafter) ofthe LSPR caused by the interaction is at the longer wavelength side ofthe absorption peak (referred to as “first peak” hereafter) of the LSPRof the metal fine-particles 9 alone. For example, when the distance L₂between a metal fine-particle 3 and a metal fine-particle 9 connected bythe binding species 7, which is the shortest distance between the metalfine-particle 3 and the metal fine-particle 9 (not shown), is less thanor equal to 3 nm, the second peak shifts toward the longer wavelengthside (the wavelength region of 600 nm to 800 nm), and when L₂ exceeds 3nm, the second peak is closer to the first peak. Therefore, the distanceL₂ between a metal fine-particle 3 and a metal fine-particle 9 ispreferably less than or equal to 3 nm.

The nano-composite 10 with the above constitution can be used inapplications such as affinity bio-sensors, and so on. FIG. 4 is aschematic illustration of application of the nano-composite 10 as anaffinity bio-sensor. At first, a nano-composite 10 is provided, whichhas a structure where metal fine-particles 9 are immobilized, via abinding species 7, on the exposed portions 3 a of metal fine-particles 3partially embedded in a matrix resin 1 and where another binding species11 (a ligand) is bonded to the surfaces of the metal fine-particles 9,as also shown in FIG. 3. Next, a sample containing an analyte 30 and anon-detection object substance 40 is made contact with thenano-composite 10 having the binding species 11 being bonded to themetal fine-particles 9. Because the binding species 11 has a specificbindability with the analyte 30, a specific binding is produced betweenthe analyte 30 and the binding species 11 through the contact. Thenon-detection object substance 40, which has no specific bindabilitywith the binding species 11, does not bind with the binding species 11.As compared with the nano-composite 10 to which no analyte 30 but onlythe binding species 11 is bonded, the nano-composite 10 to which theanalyte 30 is bonded via the binding species 11 has a change in theabsorption spectrum of the LSPR, under light irradiation. That is, thedeveloped color is changed. In this way, by detecting a change in theabsorption spectrum of the LSPR, the analyte 30 in the sample can bedetected with high sensitivity. The affinity bio-sensors utilizing LSPRdoes not need to use a label substance, and can be utilized as atechnique for bio-sensors with simple constitutions in various fields.

<Fabrication Method>

Next, the method of fabricating the nano-composite 10 of this embodimentis described. The fabrication of the nano-composite 10 includes: 1) astep of forming a resin film containing a metal ion (or metal salt), 2)a reduction step, 3) an etching step, 4) a step of immobilizing thebinding species 7, and 5) a step of immobilizing the metalfine-particles 9. Herein, a case where the matrix resin 1 constitutes apolyimide resin is described as a representative example.

1) The Step of Forming a Resin Film Containing a Metal Ion (or MetalSalt)

Firstly, a polyamic acid resin film (or polyamic acid resin layer)containing a metal ion (or metal salt) is prepared, possibly by using,for example, the casting method or the alkali modification describedbelow.

Casting Method:

A casting method includes casting, on an arbitrary substrate, a polyamicacid resin solution containing a polyamic acid resin to form a polyamicacid resin film. Any of the following casting methods (I) to (III) canbe used to form a polyamic acid resin film containing a metal ion (ormetal salt):

(I) the method of casting a coating liquid containing a polyamic acidresin and a metal compound on an arbitrary substrate to form a polyamicacid resin film containing a metal ion (or metal salt);

(II) the method of casting a polyamic acid resin solution not containinga metal ion (or metal salt) on an arbitrary substrate to form a polyamicacid resin film, and then immersing the polyamic acid resin film in asolution containing a metal ion (or metal salt), which is referred to as“metal ion solution” hereafter; and

(III) the method of immersing, in a solution containing a metal ion (ormetal salt), the polyamic acid resin film containing a metal ion (ormetal salt) as formed with the above method (I).

The casting method is advantageous over the later-described alkalimodification method, in certain aspects including: easy control of thethickness of the metal fine-particle layer 5 or the matrix resin 1, easyapplication without a limitation on the chemical structure of thepolyimide resin, and so on.

The merit of the above method (I) is that the amount of the metalcompound contained in the polyamic acid resin solution can be easilyadjusted. Thereby, for example, the amount of the metal contained in thenano-composite 10 can be easily adjusted, or a nano-composite 10containing relatively larger metal fine-particles 3 with a particlediameter D₁ above 30 nm can be easily fabricated. That is, by using theabove method (I), e.g., the particle diameter D₁ can be controlled inthe range of 30 nm to 50 nm.

The merit of the above method (II) is that the metal ion (or metal salt)is impregnated in the polyamic acid resin film as being dissolvedhomogeneously and is thereby uniformly dispersed in the polyamic acidresin film with little variation. Hence, for example, a nano-composite10 containing metal fine-particles 3 having a relatively narrowerparticle-diameter distribution can be fabricated.

The substrate used in the casting method is not particularly limited, incases where the nano-composite 10 is peeled from the substrate to beused as a sensor or the like, or in cases where the nano-composite 10utilizes the LSPR in a light-reflection manner while being attached witha substrate. In cases where the nano-composite 10 utilizes the LSPR in alight-transmission manner while being attached with a substrate, thesubstrate is preferably transparent to light, and, for example, a glasssubstrate or a transparent synthetic resin substrate, etc., can be used.Examples of the transparent synthetic resin include: polyimide resin,PET resin, acryl resin, MS resin, MBS resin, ABS resin, polycarbonateresin, silicone resin, siloxane resin, and epoxy resin, etc.

The polyamic acid resin as the precursor of a polyimide resin, which isreferred to as “precursor” hereafter, can be a well-known polyamic acidresin obtained from well-known acid anhydride and diamine. The polyamicacid resin is obtained by, for example, dissolving in an organic solventa tetracarboxylic dianhydride and a diamine in a substantially equimolarratio, and stirring at a temperature in the range of 0-100° C. for 30min to 24 hours to conduct a polymerization reaction. Regarding thereaction, it is good to dissolve the reactants in a manner such that theamount of the obtained polyamic acid resin in the organic solvent is inthe range of 5 wt % to 30 wt %, preferably in the range of 10 wt % to 20wt %. The organic solvent used in the polymerization reaction may be apolar one. Examples of the organic polar solvent include:N,N-dimethylformamide, N,N-dimethylacetamide (DMAc),N-methyl-2-pyrrolidone, 2-butanone, dimethylsulfoxide, dimethyl sulfate,cyclohexanone, dioxane, tetrahydrofuran, diglyme, and triglyme, etc.These solvents can be used in combination of two or more, and may alsobe used in part with an aromatic hydrocarbon such as xylene or toluene.

The synthesized polyamic acid resin is used in the form of a solution.It is usually advantageous to use a solution based on the reactionsolvent, but, if required, the solution can be concentrated, diluted, orreplaced by another organic solvent. A such prepared solution can beutilized as a coating liquid by an addition of a metal compound.

The polyamic resin is preferably chosen such that the polyimide resinafter the imidization has thermoplasticity and low thermalexpandability. Moreover, the polyimide resin can be exemplified as athermo-resistant resin constituted of a polymer having an imido group inits structure, such as polyimide, polyamideimide, polybenzimidazole,polyimide ester, polyetherimide, or polysiloxaneimide, etc.

Examples of the diamine suitably used to prepare the polyamic acid resininclude 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl,4,4′-diaminodiphenylether, 2′-methoxy-4,4′-diaminobenzanilide,1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene,2,2-bis[4-(4-aminophenoxyl)phenyl]propane,2,2′-dimethyl-4,4′-diaminobiphenyl, 3,3′-dihydroxy-4,4′-diaminobiphenyl,and 4,4′-diaminobenzanilide, etc. Moreover, the diamine is suitablyexemplified as 2,2-bis[4-(3-aminophenoxyl)phenyl]propane,bis[4-(4-aminophenoxyl)phenyl]sulfone,bis[4-(3-aminophenoxyl)phenyl]sulfone, bis[4-(4-aminophenoxy)]biphenyl,bis[4-(3-aminophenoxy)]biphenyl, bis[1-(4-aminophenoxy)]biphenyl,bis[1-(3-aminophenoxy)]biphenyl, bis[4-(4-aminophenoxyl)phenyl]methane,bis[4-(3-aminophenoxyl)phenyl]methane,bis[4-(4-aminophenoxyl)phenyl]ether,bis[4-(3-aminophenoxyl)phenyl]ether,bis[4-(4-aminophenoxy)]benzophenone,bis[4-(3-aminophenoxy)]benzophenone,bis[4,4′-(4-aminophenoxy)]benzanilide,bis[4,4′-(3-aminophenoxy)]benzanilide,9,9-bis[4-(4-aminophenoxyl)phenyl]fluorene, and9,9-bis[4-(3-aminophenoxyl)phenyl]fluorine, etc.

Examples of other amines include2,2-bis[4-(4-aminophenoxyl)phenyl]hexafluoropropane,2,2-bis[4-(3-aminophenoxyl)phenyl]hexafluoropropane,4,4′-methylenedi-o-toluidine, 4,4′-methylenedi-2,6-xylidine,4,4′-methylene-2,6-diethylaniline, 4,4′-diaminodiphenylpropane,3,3′-diaminodiphenylpropane, 4,4′-diaminodiphenylethane,3,3′-diaminodiphenylethane, 4,4′-diaminodiphenylmethane,3,3′-diaminodiphenylmethane, 4,4′-diaminodiphenylsulfide,3,3′-diaminodiphenylsulfide, 4,4′-diaminodiphenylsulfone,3,3′-diaminodiphenylsulfone, 4,4′-diaminodiphenylether,3,3′-diaminodiphenylether, 3,4′-diaminodiphenylether, benzidine,3,3′-diaminobiphenyl, 3,3′-dimethyl-4,4′-diaminobiphenyl,3,3′-dimethoxybenzidine, 4,4″-diamino-p-terphenyl,3,3″-diamino-p-terphenyl, m-phenylenediamine, p-phenylenediamine,2,6-diaminopyridine, 1,4-bis(4-aminophenoxy)benzene,1,3-bis(4-aminophenoxy)benzene,4,4′-[1,4-phenylenebis(1-methylethylidene)]bisaniline,4,4′-[1,3-phenylenebis(1-methylethylidene)]bisaniline,bis(p-aminocyclohexyl)methane, bis(p-β-amino-t-butylphenyl)ether,bis(p-β-methyl-δ-aminopentyl)benzene,p-bis(2-methyl-4-aminopentyl)benzene,p-bis(1,1-dimethyl-5-aminopentyl)benzene, 1,5-diaminonaphthalene,2,6-diaminonaphthalene, 2,4-bis(β-amino-t-butyl)toluene,2,4-diaminotoluene, m-xylene-2,5-diamine, p-xylene-2,5-diamine,m-xylylenediamine, p-xylylenediamine, 2,6-diaminopyridine,2,5-diaminopyridine, 2,5-diamino-1,3,4-oxadiazole, and piperazine, etc.

The particularly preferred diamine component is exemplified as one ormore diamines selected from2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB),1,3-bis(4-aminophenoxy)-2,2-dimethylpropane (DANPG),2,2-bis[4-(4-aminophenoxyl)phenyl]propane (BAPP),1,3-bis(3-aminophenoxy)benzene (APB), paraphenylenediamine (p-PDA),3,4′-diaminodiphenylether (DAPE34), and 4,4′-diaminodiphenylether(DAPE44).

Examples of the acid anhydride suitably used to prepare the polyamicacid resin include anhydrous pyromellitic acid,3,3′,4,4′-biphenyltetracarboxylic dianhydride,3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride, and4,4′-oxydiphthalic anhydride. The followings are also preferred examplesof the acid anhydride: 2,2′,3,3′-, 2,3,3′,4′- or3,3′,4,4′-benzophenonetetracarboxylic dianhydride,2,3′,3,4′-biphenyltetracarboxylic dianhydride,2,2′,3,3′-biphenyltetracarboxylic dianhydride,2,3′,3,4′-diphenylethertetracarboxylic dianhydride, andbis(2,3-dicarboxyphenyl)ether dianhydride, etc. Moreover, the followingsare also preferred examples of the acid anhydride: 3,3″,4,4″-,2,3,3″,4″- or 2,2″,3,3″-p-terphenyltetracarboxylic dianhydride,2,2-bis(2,3- or 3,4-dicarboxyphenyl)propane dianhydride, bis(2,3- or3,4-dicarboxyphenyl)methane dianhydride, bis(2,3- or3,4-dicarboxyphenyl)sulfone dianhydride, and 1,1-bis(2,3- or3,4-dicarboxyphenyl)ethane dianhydride, etc.

The particularly preferred acid anhydride is exemplified as one or moreacid anhydrides selected from anhydrous pyromellitic acid (PMDA),3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA),3,3′,4,4′-benzophenonetetracarboxylic dianhydride (BTDA), and3,3′,4,4′-diphenylsulfonetetracarboxylic dianhydride (DSDA).

The diamines or the acid anhydrides can be used alone or in combinationof two or more species. Moreover, diamines and acid anhydrides otherthan the above mentioned ones can also been used in combination.

In this embodiment, to prepare a coating liquid containing a metalcompound or a polyamic acid resin solution not containing a metal ion(or metal salt), a commercially available solution containing a polyamicacid resin can be suitably used. Examples of the polyamic acid solutionserving as a precursor of a thermoplastic polyimide resin include thethermoplastic polyamic acid resin varnishes SP1-200N™, SPI-300N™ andSPI-1000G™ produced by Nippon Steel Chemical Co., Ltd.), and Torayneece#3000™ produced by Toray Industries, Inc., etc. Moreover, examples ofthe polyamic acid solution serving as a precursor of a non-thermoplasticpolyimide resin include the non-thermoplastic polyamic acid resinvarnishes U-varnish-A™ and U-varnish-S™ produced by UBE Industries,Ltd., etc.

When the nano-composite 10 is suitably used in an application utilizingLSPR of the light transmission type, for example, it is preferred to usea transparent or colorless polyimide resin, wherein an intra- orinter-molecular charge-transfer (CT) complex is difficult to form, suchas an aromatic polyimide resin having a substituent with a bulky stericstructure, an alicyclic polyimide resin, a fluoro-polyimide resin, or asilicon-polyimide resin, etc.

The above substituent with a bulky steric structure may have, forexample, a fluorene skeleton or an admantane skeleton, etc. In thearomatic polyimide resin, such a substituent with a bulky stericstructure may be located on any one of the acid anhydride residue andthe diamine residue, or on both of them. A diamine having a substituentwith a bulky steric structure can be exemplified by9,9-bis(4-aminophenyl)fluorene, etc.

The alicyclic polyimide resin is a resin formed by polymerizing analicyclic acid anhydride and an alicyclic diamine. Moreover, thealicyclic polyimide resin can also be obtained by hydrogenating anaromatic polyimide resin.

The fluoro-polyimide resin is a resin formed by polymerizing an acidanhydride and/or a diamine in which a monovalent element bonded to acarbon of, for example, alkyl or phenyl, etc., is substituted byfluorine, a perfluoroalkyl group, a perfluoroaryl group, aperfluoroalkoxy group, or a perfluorophenoxy group, etc. Though themonovalent element can be totally or partially substituted by fluorineatoms, it is preferred that 50% or more of the monovalent element issubstituted.

The silicon-polyimide resin is a resin obtained by polymerizing asilicon-containing diamine and an acid anhydride.

It is preferred that such a transparent polyimide resin, for example ata thickness of 10 μm, has a transmittance greater than or equal to 80%at the wavelength 400 nm, and a mean transmittance of visible lightgreater than or equal to 90%.

Among the above polyimide resins, the fluoro-polyimide resin with aparticularly high transparency is preferred. A polyimide resin with aconstituting unit expressed by general formula (1) can be used as thefluoro-polyimide resin. Herein, in general formula (1), Ar₁ is atetravalent aromatic group expressed by formula (2), (3) or (4), Ar₂ isa divalent aromatic group expressed by formula (5), (6), (7) or (8), andp is the repetition number of the constituting unit.

Moreover, each R is independently a fluorine atom or a perfluoroalkylgroup, Y is a divalent group expressed by the following structuralformulae, R₁ is a perfluoroalkylene group, and n is a number of 1 to 19.

—O—,—CO—,—SO₂—,

—R₁—,—OR₁—,—R₁O—,

—(OR₁)_(n)—,—(R₁O)_(n)—,—(OR₁O)_(n)— or

—O—CO—R₁—CO—O—

Because in the above general formula (1) Ar₂ can be deemed an amineresidue and Ar₁ be deemed an acid anhydride residue, the preferredfluoro-polyimide resin is described by exemplifying the diamine, and theacid anhydride or a tetracarboxylic acid, an acid chloride or anesterfied compound that can be utilized equivalently (referred to as“acid anhydride, etc.” hereafter). However, the fluoro-polyimide resinis not limited to be obtained from the diamines and the acid anhydrides,etc., described herein.

The raw-material diamine corresponding to Ar₂ can be any amine if onlyany monovalent element bonded to the carbon of an alkyl group or aphenyl ring, etc., other than the amino group in the molecule, isfluorine or a perfluoroalkyl group. Such diamine can be exemplified as3,4,5,6-tetrafluoro-1,2-phenylenediamine,2,4,5,6-tetrafluoro-1,3-phenylenediamine,2,3,5,6-tetrafluoro-1,4-phenylenediamine,4,4′-diaminooctafluorobiphenyl,bis(2,3,5,6-tetrafluoro-4-aminophenyl)ether,bis(2,3,5,6-tetrafluoro-4-aminophenyl)sulfone,hexafluoro-2,2′-bistrifluoromethyl-4,4′-diaminobiphenyl, or2,2-bis(trifluoromethyl)-4,4′-diaminobiphenyl, etc.

Examples of the raw-material acid anhydride corresponding to Ar₁ include1,4-difluoropyromellitic acid, 1-trifluoromethyl-4-fluoropyromelliticacid, 1,4-di(trifluoromethyl)pyromellitic acid,1,4-di(pentafluoroethyl)pyromellitic acid,hexafluoro-3,3′,4,4′-bisphenyltetracarboxylic acid,hexafluoro-3,3′,4,4′-benzophenonetetracarboxylic acid,2,2-bis(3,4-dicarboxytrifluorophenyl)hexafluoropropane,1,3-bis(3,4-dicarboxytrifluorophenyl)hexafluoropropane,1,4-bis(3,4-dicarboxytrifluorophenoxy)tetrafluorobenzene,hexafluoro-3,3′,4,4′-oxybisphthalic acid, and4,4′-(hexafluoroisopropylidene)diphthalic acid, etc.

As the metal compound contained in the coating liquid together with thepolyamic acid resin prepared for the above method (I), or the metalcompound contained in the solution containing a metal ion (or metalsalt) prepared for the above method (II), a compound that contains theabove metal species constituting the metal fine-particles 3 can be usedwithout a particular limitation. As the metal compound, a salt or anorganic carbonyl complex, etc., of the above metal can be used. Themetal salt can be exemplified as a hydrochloric salt, a sulfate salt, anacetate salt, an oxalate salt, or a citrate salt, etc. Moreover, theorganic carbonyl compound obtained by forming an organic carbonylcomplex from the above metal species can be exemplified asacetylacetone, benzoylacetone, a β-diketone such as dibenzoylmethane, ora β-ketocarboxylate ester such as ethyl acetoacetate, etc.

Preferred specific examples of the metal compound may include: H[AuCl₄],Na[AuCl₄], AuI, AuCl, AuCl₃, AuBr₃, NH₄[AuCl₄].n2H₂O, Ag(CH₃COO), AgCl,AgClO₄, Ag₂CO₃, AgI, Ag₂SO₄, AgNO₃, Ni(CH₃COO)₂, Cu(CH₃COO)₂, CuSO₄,CuCl₂, CuBr₂, Cu(NH₄)₂Cl₄, CuI, Cu(NO₃)₂, Cu(CH₃COCH₂COCH₃)₂, CoCl₂,CoCO₃, CoSO₄, C(NOO₃)₂, NiSO₄, NiCO₃, NiCl₂, NiBr₂, Ni(NO₃)₂, NiC₂O₄,Ni(H₂PO₂)₂, Ni(CH₃COCH₂COCH₃)₂, Pd(CH₃COO)₂, PdSO₄, PdCO₃, PdCl₂, PdBr₂,Pd(NO₃)₂, Pd(CH₃COCH₂COCH₃)₂, SnCl₂, IrCl₃, and RhCl₃, etc.

In the coating liquid containing a polyamic acid resin prepared for theabove method (1) and a metal compound, the metal ion formed bydissociation of the metal compound may cause a three-dimensionalcrosslinking reaction between the polyamic acid resin, depending on thespecies of the metal. Hence, the coating liquid may be thickened/gelatedas time goes on and may be difficult to use. To prevent suchthickening/gelation, it is preferred to add in the coating liquid aviscosity adjusting agent as a stabilizing agent. By adding theviscosity adjusting agent, the metal ion in the coating liquid forms achelate complex with the viscosity adjusting agent instead but not withthe polyamic acid resin. In this way, three-dimensional crosslinkingbetween the polyamic acid resin and the metal ion is blocked by theviscosity adjusting agent, and the thickening/gelation is inhibited.

As the viscosity adjusting agent, it is preferred to select alow-molecular organic compound that has a high reactivity with the metalion, i.e., allows the formation of a metal complex. The molecular weightof the low-molecular organic compound is preferably within the range of50 to 300. Specific examples of such viscosity adjusting agents mayinclude acetylacetone, ethyl acetoacetate, pyridine, imidazole, andpicoline, etc. Moreover, the addition amount of the viscosity adjustingagent relative to 1 mole of the formed chelate complex compound ispreferably in the range of 1 mole to 50 moles and more preferably in therange of 2 moles to 20 moles.

The amount of the metal compound in the coating liquid, relative to 100parts by weight of the combination of the polyamic acid resin, the metalcompound and the viscosity adjusting agent, is made in the range of 3 wt% to 80 wt % and preferably in the range of 20 wt % to 60 wt %. If theamount of the metal compound is less than 3 parts by weight, separationof the metal fine-particles 3 is insufficient. If the amount exceeds 80parts by weight, the metal salt that cannot be dissolved in the coatingliquid precipitates, so that the metal fine-particles 3 tend toaggregate easily.

Moreover, in the coating liquid, arbitrary component other than theabove ones, such as a leveling agent, an anti-foaming agent, an adhesionpromoter or a crosslinking agent, etc., may be added.

The method of coating the coating liquid containing a metal compound orthe polyamic resin solution not containing a metal ion (or metal salt)is not particularly limited, and is possibly a coating method using acoater such as a comma, a die, a knife or a lip, etc. However, among thecoaters, the preferred ones are spin coater, gravure coater, and barcoater, etc., that allows the formation of a uniform coated film (orpolyamic acid resin film) to easily control the thickness of the matrixresin 1 in a high precision.

Moreover, in the metal ion solution used in the above method (II), themetal compound in contained preferably in the range of 30 mM to 300 mM,more preferably in the range of 50 mM to 100 mM. If the concentration ofthe metal compound is less than 30 mM, the time required to impregnatingthe metal ion solution in the polyamic acid resin film is overly long,which is not preferred. If the concentration exceeds 300 mM, it isworried that the surface of the polyamic acid resin film is eroded(dissolved).

In addition to the metal compound, the metal ion solution can alsocontain a component for adjusting the pH value, such as a buffersolution, etc.

The impregnation method is not particularly limited as long as it makesthe surface of the polyamic acid resin film contact with the metal ionsolution, and can be a well known method, such as a dipping method, aspray method, a brush coating method or a printing method, etc.

The impregnation temperature is within the range of 0-100° C., and ispreferably a normal temperature around 20-40° C. Moreover, when thedipping method is applied, the impregnation time is, for example,preferably from 1 min to 5 hours and more preferably from 5 minutes to 2hours. If the impregnation time is less than 1 min, impregnation of themetal ion solution in the polyamic acid resin film is insufficient. Onthe contrary, if the impregnation time exceeds 5 hours, the degree ofthe impregnation of the metal ion solution in the polyamic acid resinfilm tends to be unvaried substantially.

After the coating liquid containing a metal compound or the polyamicacid resin solution not containing a metal ion (or metal salt) iscoated, drying is conducted to form a polyamic acid resin film. Duringthe drying, the temperature is controlled such that the imidizationcaused by dehydration and ring closure of the polyamic acid resin is notcompleted. The drying method is not particularly limited, and the dryingmay be conducted, for example, at a temperature in the range of 60-200°C. for 1 min to 60 min, and preferably at a temperature in the range of60-150° C. It does not matter if a part of the structure of the polyamicacid resin in the dried polyamic acid resin film is imidized. However,it is feasible that the imidization ratio is 50% or less and morepreferably 20% or less and 50% or more of the polyamic acid structureremains. Moreover, the imidization ratio of the polyamic acid resin canbe calculated, while a Fourier-Transform IR spectroscope (a commerciallyavailable product is, for example, FT/IR620 manufactured by JASCOCorporation) is used to measure the IR absorption spectrum of the filmwith a transmission-type method, from the absorbance at 1710 cm⁻¹ due tothe imide group, with the absorbance at 1000 cm⁻¹ due to the C—H bond onthe benzene ring as a reference.

The polyamic acid resin film may be a single layer, or a laminatedstructure formed from a plurality of polyamic acid resin films. In thecase of multiple layers, the film can be formed by coating, on layers ofpolyamic acid resins having different constituting components, otherpolyamic acid resin(s) in sequence. When the polyamic acid resin filmincludes 3 or more layers, the polyamic acid resin of the sameconstitution may be used 2 or more times. When the film has a simple2-layer or single-layer structure, especially a single-layer structure,it is beneficial in the industry.

Moreover, after a single layer or multiple layers of polyamic acidresins are laminated on a sheet-like support member and then imidized toform a single layer or multiple layers of polyimide resins, it is alsopossible to further form a polyamic acid resin film on the same. In sucha case, to promote the adhesion between the polyimide resin layer andthe polyamic acid resin film, the surface of the polyimide resin layeris preferably surface-treated by plasma. With such plasma surfacetreatment, the surface of the polyimide resin layer can be roughened, orthe chemical structure of the surface is altered. Thereby, thewettability of the surface of the polyimide resin layer, the affinitythereof with the polyamic acid resin solution is raised, and thepolyamic acid resin film can be stably maintained on the surface.

Alkali Modification Method

The alkali modification method includes modifying the surface of apolyimide film by an alkali to form a polyamic acid resin layer and thenimpregnating a metal ion solution in the polyamic acid resin layer. Theused polyimide resin is the same as that used in the above castingmethod, so its description is omitted.

Because the metal ion (or metal salt) is impregnated in the polyamicacid resin layer in a state of being homogeneously dissolved in themetal ion solution and thereby uniformly dispersed in the polyamic acidresin layer with little concentration variation, the alkali modificationhas, for example, the following merits etc. A nano-composite 10containing metal fine-particles 3 with a relatively narrowerparticle-diameter distribution can be made. An integral-typenano-composite 10 having a high adhesion with a polyimide film substratecan be made. When a nano-composite 10 is being made at the surface sideof a polyimide film, the same process can be conducted at the back sideof the polyimide film simultaneously. Or, the metal ion in the metal ionsolution can be easily ion-exchanged with the salt of the alkali metaland the carboxylate groups at the terminals of the polyimide chainscaused by the aqueous alkali solution, so that the impregnation time canbe shortened.

The aqueous alkali solution for treating the polyimide film ispreferably an aqueous solution of sodium hydroxide or potassiumhydroxide having a concentration in the range of 0.5 wt % to 50 wt % anda liquid temperature in the range of 5-80° C. The aqueous alkalisolution can be suitably applied with a dipping method, a spray methodor brush coating method, etc. In a case using the dipping method, forexample, it is effective to treat the polyimide film by the aqueousalkali solution for 10 sec to 60 min. It is preferred that the surfaceof the polyimide film is treated, by an aqueous alkali solution with aconcentration in the range of 1 wt % to 30 wt % and a liquid temperaturein the range of 25-60° C., for 30 sec to 10 min. The treatment conditioncan be suitably changed depending on the structure of the polyimidefilm. In general, when the concentration of the aqueous alkali solutionis lower, the treatment time of the polyimide film becomes longer.Moreover, when the liquid temperature of the aqueous alkali solution ishigher, the treatment time is shortened.

By the treatment with the aqueous alkali solution, the aqueous alkalisolution penetrates from the surface side of the polyimide film tomodify the polyimide resin. The modification reaction caused by thealkali treatment is considered to be based on hydrolysis of the imidobonds. The thickness of the alkali-treated layer formed by the alkalitreatment is preferably in the range of 1/5000 to ½, more preferably inthe range of 1/3000 to ⅕, of the thickness of the polyimide film. Inanother view point, the thickness of the alkali-treated layer issuitably in the range of 0.005 μm to 3.0 μm, preferably in the range of0.05 μm to 2.0 μm, and more preferably in the range of 0.1 μm to 1.0 μm.By setting the thickness in such range, the formation of the metalfine-particles 3 is facilitated. If the thickness of the alkali-treatedlayer is less than the lower limit (0.005 μm), it is difficult tosufficiently impregnate the metal ion. On the other hand, in thetreatment of the polyimide resin with the aqueous alkali solution, theoutmost portion of the polyimide resin tends to be dissolvedsimultaneously when the imido-ring of the polyimide resin is opened, sothat the above upper limit (3.0 μm) is difficult to exceed. Moreover,when the metal fine-particles 3 are to be substantially dispersedtwo-dimensionally, the thickness of the alkali-treated layer formed bythe alkali treatment is preferably in the range of 1/5000 to 1/20, morepreferably in the range of 1/500 to 1/50, of the thickness of thepolyimide film. In another view point, the thickness of thealkali-treated layer is suitably in the range of 20 nm to 150 nm,preferably in the range of 50 nm to 150 nm, and more preferably in therange of 100 nm to 120 nm. By setting the thickness in such range, theformation of the metal fine-particles 3 is facilitated.

In view of the ease of the modification of the polyimide film with theaqueous alkali solution, it is desired to select a polyimide film havinga high water absorption ratio. The water absorption ratio of thepolyimide film is preferably 0.1% or more, and more preferably 0.2% ormore. If the water absorption ratio is less than 0.1%, the modificationis insufficient, or the modification time is required to be wellincreased, which is not good.

Moreover, because the degree of the modification treatment of thepolyimide film by the aqueous alkali solution varies when the chemicalstructure of the polyimide resin constituting the polyimide film isdifferent, it is preferred to select a polyimide film easily subjectedto the modification treatment. Examples of such polyimide film suitablysubjected to a modification treatment with an aqueous alkali solutioninclude: a polyimide film having ester bonds in its structure, and apolyimide film using anhydrous pyromellitic acid as one of the acidanhydride monomers. The amount of the anhydrous pyromellitic acidrelative to 100 moles of the acid anhydride component is preferably 50moles or more and more preferably 60 moles or more.

It is also feasible to simultaneously modify both sides of the polyimidefilm with the alkali treatment, depending on the application. Apolyimide resin layer constituted of a polyimide resin with a lowthermal expandability, to which the alkali treatment is particularlyeffective, is suitable. A polyimide resin with a low thermalexpandability has a good familiarity (wettability) with respect to theaqueous alkali solution, so that the ring opening reaction of the imidering is easily induced.

In the alkali-treated layer, a salt of the alkali metal from the aqueousalkali solution and the terminal carboxyl groups of the polyimide resin,etc., are formed. The alkali metal carboxylate salt of the carboxyl canbe substituted by the salt of the metal ion through the metal ionsolution impregnation treatment in the subsequent metal ion solutionimpregnation step, so there is no problem even if the salt of the metalion exists before the subsequent metal ion solution impregnation step isconducted. Moreover, the surface layer of the polyimide resin turned tobe alkaline may be neutralized by an aqueous acid solution. The aqueousacid solution can be arbitrary aqueous solution as long as it is acidic,but is particularly preferably an aqueous hydrochloric acid solution oran aqueous sulfuric acid solution. Moreover, the concentration of theaqueous acid solution is suitably in the range of 0.5 wt % to 50 wt %,preferably in the range of 0.5 wt % to 5 wt %. It is more preferred thatthe pH value of the aqueous acid solution is 2 or less. After beingcleaned by the aqueous acid solution, washed by water and then dried,the treated polyimide film is provided to the subsequent metal ionsolution impregnation step.

The polyimide film being formed with an alkali-modified layer issubjected to the impregnation of a metal ion solution and then dried toform a layer containing a metal ion (or metal salt). With theimpregnation treatment, the carboxyl group present in thealkali-modified layer is made into a metal carboxylate salt.

The metal ion and the metal compound, and the metal ion solution used inthe impregnation step can be the same as those used in the above castingmethod.

The impregnation method is not particularly limited as long as the metalion solution is able to contact the surface of the alkali-modifiedlayer, and can be a well known method. For example, a dipping method, aspray method, a brush coating method or a printing method, etc., can beused. The impregnation temperature is in the range of 0-100° C., and ispreferably a room temperature around 20-40° C. Moreover, when thedipping method is used, the impregnation time is, for example,preferably 1 min to 5 hours and more preferably 5 min to 2 hours.

The film is dried after the impregnation. The drying method is notparticularly limited, and may be, for example, natural drying,blow-drying using an air gun, or drying with an oven, etc. The dryingcondition is 10-150° C. for 5 sec to 60 min, preferably 25-150° C. for10 sec to 30 min, and more preferably 30-120° C. for 1-10 min.

In “the polyamic acid resin film or the polyamic acid resin layercontaining a metal ion or a metal salt” (referred to as “a polyamic acidresin layer containing a metal ion” hereafter) formed by the abovecasting method or alkali modification method, the metal ion is adsorbedon the carboxyl group due to the interaction between the metal ion andthe carboxyl group of the polyamic acid resin, and a complex is formed.Such a phenomenon has an effect of uniformizing the concentrationdistribution of the metal ion in the polyamic acid resin layercontaining a metal ion. Hence, there is an effect that an unevendistribution or aggregation of the metal fine-particles 3 separated fromthe matrix resin 1 is prevented, and metal fine-particles 3 having auniform shape are separated from the resin in a uniform distribution.

(2) Reduction Step:

In the reduction step, the above obtained polyamic acid resin layercontaining a metal ion is thermally treated to reduce the metal ion (ormetal salt) and separate metal fine-particles 3, preferably at atemperature of 140° C. or higher, more preferably at a temperature inthe range of 160-450° C. and even more preferably in the range of200-400° C. If the temperature of the thermal treatment is lower than140° C., the reduction of the metal ion (or metal salt) is insufficient,and it is difficult to make the mean particle diameter D_(1A) of themetal fine-particles 3 greater than or equal to the lower limit (3 nm).Moreover, if the temperature of the thermal treatment is lower than 140°C., in the matrix resin 1, thermal diffusion of the metal fine-particles3 being separated due to the reduction is not induced sufficiently.Further, if the temperature of the thermal treatment is lower than 140°C., in cases where a polyimide resin is used as the matrix resin 1, theimidization of the precursor of the polyimide resin is insufficient, anda re-heating step for imidization is required. On the contrary, if thetemperature of the thermal treatment is above 450° C., the matrix resin1 is decomposed thermally, so that new absorption due to thedecomposition of the matrix resin 1 is easily produced in addition tothe absorption due to the LSPR, or the distance between neighboringmetal fine-particles 3 becomes small to easily cause an interactionbetween neighboring metal fine-particles 3, etc. Therefore, theabsorption spectrum due to the LSPR is broadened. Moreover, the time ofthe thermal treatment can be determined according to the targetinter-particle distance and further according to the temperature of thethermal treatment or the amount of the metal ion (or metal salt)contained in the polyamic acid layer. For example, the time can be setin the range of 10 min to 180 min when the temperature of the thermaltreatment is 200° C., or in the range of 1 min to 60 min when thetemperature of the thermal treatment is 400° C.

The particle diameter D₁ and the inter-particle distance L₁ of the metalfine-particles 3 can be controlled based in the heating temperature andthe heating time in the reduction step, and the amount of the metal ion(or metal salt) contained in the matrix resin 1 or its precursor. Theinventors have discovered that when the heating temperature and theheating time in the thermal reduction are fixed, the particle diameterD₁ of the separated metal fine-particles 3 is changed if the absoluteamount of the metal ion (or metal salt) contained in the matrix resin 1or its precursor is changed. Moreover, there was also a discovery thatwhen the thermal reduction is conducted without controlling the heatingtemperature and the heating time, the inter-particle distance L₁ becomessmaller than the particle diameter D_(1L) of the larger one ofneighboring metal fine-particles 3, or the metal fine-particles 3aggregate on the surface of the matrix resin 1 to form islandstructures.

In view of the above discoveries, it is known that the particle diameterD₁ of the metal fine-particles can be controlled by controlling theheating temperature, and the inter-particle distance L₁ can becontrolled by controlling the heating time. These aspects will bespecifically described later in the example. For example, when gold ioncontained in an amount of 18 wt % per unit volume (cm³) [5.2 μg per unitarea (cm²)] in a polyamic acid resin (a precursor resin of the matrixresin 1) of 200 nm thick is thermally reduced in the atmosphere, theparticle diameter D₁ and the inter-particle distance L₁ of the metalfine-particles formed through the thermal reduction are varied accordingto the heating temperature and the heating time. Specifically, theparticle diameter D₁ is about 9 nm (the mean particle diameter D_(1A) isabout 9 nm) by a treatment at 200° C. for 10 min, is about 13 nm (themean particle diameter D_(1A) is about 13 nm) by a treatment at 300° C.for 3 min, or is about 15 nm (the mean particle diameter D_(1A) is about15 nm) by a treatment at 400° C. for 1 min. In any of the cases, thenano-composite is formed in a manner such that the distance between anypair of neighboring metal gold fine-particles is greater than or equalto the particle diameter D_(1L) of the larger one of the pair ofneighboring metal gold fine-particles, or is approximately close to theparticle diameter D_(1L). Based on such an example, by furthercontrolling the thickness of the metal fine-particle layer 5 in theabove range, a nano-composite 10 meeting the above requirements can beformed.

Moreover, based on the above discoveries, for example, the thermaltreatment in the reduction step can be conducted in multiple stages. Forexample, it is possible to conduct a particle-diameter controlling stepthat grows the metal fine-particles 3 to a predetermined particlediameter D₁ at a first heating temperature, and an inter-particledistance controlling step that maintains the inter-particle distance L₁of the metal fine-particles 3 in a predetermined range at a secondheating temperature being the same as or different from the firstheating temperature. In this way, by adjusting the first and the secondheating temperatures and the heating time, the particle diameter D₁ andthe inter-particle distance L₁ can be controlled more precisely.

The reasons that thermal reduction is adopted as the reduction methodinclude industrial merits, such as, that the particle diameter D₁ andthe inter-particle distance L₁ can be controlled more easily bycontrolling the treatment condition (especially the heating temperatureand the heating time), that it can be coped with a simple equipmentwithout a particular limitation from the lab scale to the productionscale, and that it can be coped with in a single-piece manner or acontinuous manner without special efforts, etc. The thermal reductioncan be conducted, for example, in an atmosphere of an inert gas such asAr or N₂ etc., in a vacuum of 1-5 kPa, or in the atmosphere. Thereduction method is not suitably a vapor reduction method using areductive gas such as hydrogen, or a light reduction method. In vaporreduction, metal fine-particles 3 are not present near the surface ofthe matrix resin 1, and thermal decomposition of the matrix resin 1 isenhanced by the reductive gas, so the inter-particle distance of themetal fine-particles 3 is difficult to control. Moreover, in lightreduction, a variation in the density of the metal fine-particles 3 fromnear the surface to the deeper portion of the matrix resin 1 is easilycaused by the light transparency of the matrix resin 1; so not only theparticle diameter D₁ and the inter-particle distance L₁ of the metalfine-particles 3 are difficult to control, but also and the reductionefficiency is low.

In the reduction step, the imidization of the polyamic acid resin can becompleted by utilizing the heat utilized in the reduction treatment, sothat the process from the separation of the metal fine-particles 3 tothe imidization can be conducted in one pot, and the manufacturingprocess can be simplified.

In the thermal reduction, the metal ion (or metal salt) existing in thematrix resin 1 or its precursor is reduced, and respective metalfine-particles 3 can be separated independently due to thermaldiffusion. Such formed metal fine-particles 3 are in a state that theinter-particle distance L₁ is kept equal to or larger than apredetermined value, and also have an approximately uniform shape, whilethe metal fine-particles 3 are not unevenly dispersed in the matrixresin 1. Particularly, when the metal ion (or metal salt) in thepolyamic acid resin layer containing a metal ion is adsorbed by thecarboxyl groups of the polyamic acid resin to form a complex, anintermediate of the nano-composite, in which the shape and the particlediameter D₁ of the metal fine-particles 3 are uniformized and eventuallythe metal fine-particles 3 are uniformly separated and dispersed in thematrix resin 1 in an approximately uniform inter-particle distance L₁,can be obtained. Moreover, the particle diameter D₁ and the distributionstate of the metal fine-particles 3 in the matrix resin 1 can becontrolled by controlling the constituting unit of the resinconstituting the matrix resin 1, or by controlling the absolute amountof the metal ion (or metal salt) and the volume fraction of the metalfine-particles 3.

(3) Etching Step:

In the etching step, a part of the metal fine-particles 3 existing inthe matrix resin 1 are exposed out of the surface of the matrix resin 1.The etching step is conducted by, for example, etching away a surfacelayer of the matrix resin 1 in the intermediate of the nano-compositethat is at the side where the metal fine-particles 3 are to be exposed.The etching method is, for example, a wet etching method using ahydrazide-series solution or an alkali solution, or a dry etching methodutilizing a plasma treatment.

Regarding the wet etching method, as a matrix resin 1 that can besuitably etched by, for example, an alkali solution, it is desired toselect a resin having a high water absorption ratio, in view of the easeof the penetration of the etching solution. The water absorption ratiois preferably 0.1% or more and more preferably 0.2% or more.

Regarding the dry etching method, as a matrix resin 1 that can besuitably etched by, for example, plasma, it is desired to select a resinhaving a polar group such as —OH, —SH, —O—, —S—, —SO—, —NH—, —CO—, —CN,—P═O, —PO—, —SO₂—, —CONH— or —SO₃H, etc., in view of the high reactivitywith the gas in the plasma state. Moreover, in another viewpoint, as inthe case were the etching utilizes an alkali solution, it is desired toselect a matrix resin 1 having a high water absorption ratio, which ispreferably 0.1% or more and more preferably 0.2% or more.

(4) Step of Immobilizing the Binding Species:

In the step of immobilizing the binding species 7, the binding species 7is immobilized on the surfaces of the portions 3 a of the metalfine-particles 3 exposed outside of the matrix resin 1. The step ofimmobilizing the binding species 7 can be conducted by having thebinding species 7 to contact with the surfaces of the exposed portions 3a of the metal fine-particles 3. For example, it is preferably toconduct a surface treatment of the metal fine-particles 3 using atreating liquid obtained by dissolving the binding species 7 in asolvent. The solvent for dissolving the binding species 7 can use, butis not limited thereto, water, C₁-C₈ hydrocarbon alcohols such asmethanol, ethanol, propanol, isopropanol, butanol, t-butanol, pentanol,hexanol, heptanol and octanol, etc., C₃-C₆ hydrocarbon ketones such asacetone, propanone, methylethyl ketone, pentanone, hexanone,methylisobutyl ketone and cyclohexanone, etc., C₄-C₁₂ hydrocarbon etherssuch as diethylether, ethylene glycol dimethylether, diethylene glycoldimethylether, diethylene glycol diethylether, diethylene glycoldibutylether and tetrahydrofuran, etc., C₃-C₇ hydrocarbon esters such asmethyl acetate, ethyl acetate, propyl acetate, butyl acetate,γ-butyrolactone and diethyl malonate, etc., C₃-C₆ amides such asdimethylformamide, dimethylacetoamide, tetramethylurea andhexamethylphosphoric triamide, etc., C₂ sulfoxides such asdimethylsulfoxide, etc., C₁-C₆ halogen-containing compounds such aschloromethane, bromomethane, dichloromethane, chloroform, carbontetrachloride, dichloroethane, 1,2-dichloroethane, 1,4-dichlorobutane,trichloroethane, chlorobenzene and o-dichlorobenzene, etc., and C₄-C₈hydrocarbon compounds such as butane, hexane, heptane, octane, benzene,toluene and xylene, etc.

The concentration of the binding species 7 in the treating liquid ispreferably from 0.0001 M (mol/L) to 1 M, for example. Although a lowconcentration leads to a merit that a small amount of remaining bindingspecies 7 is bonded to the surface of the metal fine-particles 3, theconcentration is more preferably from 0.005 M to 0.05 M.

In a case where the surfaces of the metal fine-particles 3 are to betreated by the above treating liquid, the treatment method is notlimited as long as the treating liquid can contact the exposed portions3 a of the metal fine-particles 3, while a uniform contact is preferred.For example, the metal fine-particles 3 having the exposed portions 3 amay be immersed in the treating liquid together with the matrix resin 1,or the treating liquid may be sprinkled to the exposed portions 3 a ofthe metal fine-particles 3 in the matrix resin 1 by spraying, etc., orthe treating liquid may be coated using a suitable tool. Moreover, thetemperature of the treating liquid at this moment is not particularlylimited, and is preferably 20° C. or lower, more preferably in the rangeof −20° C. to 20° C. and desirably in the range of −10° C. to 20° C. Bysetting the temperature of the treating liquid to be 20° C. or lower,the direct bonding of the binding species 7 to the matrix resin 1 isinhibited, and the binding species 7 can be selectively bonded to theexposed portions 3 a of the metal fine-particles 3. Hence, by settingthe temperature of the treating liquid to be 20° C. or lower, the metalfine-particles 9 are prevented from being eventually immobilized on thesurface of the matrix resin 1 via the binding species 7 and formingaggregates to degrade the LSPR effect. Moreover, when the surfacetreatment adopts the immersion method, for example, the immersion timeis preferably from 1 min to 24 hours.

After the surface treatment is finished, it is preferred to conduct acleaning step that uses an organic solvent to dissolve and remove theexcess binding species 7 adhering to the surfaces of the metalfine-particles 3. The organic solvent used in the cleaning step can beone capable of dissolving the binding species 7. Examples of thesolvents can be the above exemplified solvents for dissolving thebinding species 7.

In the cleaning step, the method of cleaning the surfaces of the metalfine-particles 3 by the organic solvent is not limited. It is possibleto immerse the metal fine-particles 3 in the organic solvent, tosprinkle the organic solvent by spraying, etc., to flush the metalfine-particles 3, or to soak a suitable material in the organic solventand wipe the metal fine-particles 3 with the material. In this cleaningstep, though the excess binding species 7 adhering to the surfaces ofthe metal fine-particles 3 is dissolved and removed, the binding species7 is not entirely removed. It is advantageous that the binding species 7is removed by the cleaning to an extent that the film of the bindingspecies 7 on the surfaces of the metal fine-particles 3 hasapproximately the thickness of a molecular mono-film. In a method toachieve this, a water cleaning step is conducted before the abovecleaning step, the above cleaning step is conducted, and then anotherwater cleaning step is conducted. The temperature of the organic solventin the above cleaning step at this moment is preferably from 0° C. to100° C. and more preferably in the range of 5-50° C. Moreover, thecleaning time is preferably from 1 sec to 1000 sec and more preferablyin the range of 3 sec to 600 sec. The amount of the organic solvent usedis preferably from 1 L to 500 L, more preferably in the range of 3 L to50 L, per 1 m² of the surface area of the nano-composite 10.

Moreover, if required, it is preferred to remove the binding species 7adhering to the surface of the matrix resin 1 by an alkali solution. Thealkali solution used at this moment preferably has a concentration from10 mM (mmol/L) to 500 mM and a temperature from 0° C. to 50° C. When thealkali solution is used for immersion, for example, the immersion timeis preferably from 5 sec to 3 min.

(5) Step of Immobilizing the Metal Fine-Particles 9:

In the step of immobilizing the metal fine-particles 9, the metalfine-particles 9 are bonded to the binding species 7 and indirectlyimmobilized on the metal fine-particles 3 via the binding species 7. Thestep of immobilizing the metal fine-particles 9 can be conducted bymaking the metal fine-particles 9 contact with the binding species 7that have been immobilized on the metal fine-particles 3. The method ofcontacting the metal fine-particles 9 with the binding species 7 is notlimited. For example, it is possible to immerse the semi-finishednano-composite with the binding species 7 bonded to the metalfine-particles 3, together with the matrix resin 1, in a treating liquidcontaining the metal fine-particles 9. It is also possible to sprinklethe treating liquid containing the metal fine-particles 9 on thesemi-finished nano-composite by spraying, etc., or to coat the treatingliquid with a suitable tool. Herein, for example, a metal colloidalsolution can be well used as the treating liquid. In view of raising theefficiency of the bonding between the binding species 7 and the metalfine-particles 9, the immersion method is preferred among the abovemethods. In the immersion method, for example, a metal colloidalsolution containing the metal fine-particles 9 is prepared, and anano-composite 10 with metal fine-particles 9 bonded to the bindingspecies 7 can be obtained by immersing, in the metal colloidal solution,the semi-finished nano-composite having the metal fine-particles 3 andthe binding species 7. Moreover, when the immersion method is adopted,it is preferred that, for example, the treatment temperature is from 0°C. to 50° C. and the immersion time is from 1 min to 24 hours. After themetal fine-particles 9 are immobilized, it is feasible to conduct acleaning step using pure water, etc., if required.

With the above steps, a nano-composite 10 having the constitution asshown in FIG. 1 can be fabricated. Moreover, even when the matrix resin1 uses a resin other than the polyimide resin (polyamic acid resin),such a nano-composite 10 can also be fabricated based on the abovefabrication method.

In the fabrication of the nano-composite 10, in addition to the abovesteps (1) to (4), arbitrary step can be conducted. For example, abinding species 11 can be further added to the metal fine-particles 9 ofthe nano-composite 10. In this case, the immobilization of the bindingspecies 11 on the metal fine-particles 9 can be performed according tothe step (4) of immobilizing the binding species. When a treating liquidobtained by dissolving the binding species 11 in a solvent is used totreat the surfaces of the metal fine-particles 9, the temperature is notparticularly limited, and can be set in the range of 0-50° C., forexample.

EXAMPLES

Next, this invention will be described specifically with examples, whichare not intended to put any limitation on this invention. Moreover, anyof the various measurements and evaluations is based on thecorresponding one described below, as long as it is not specified in theexamples of this invention.

[Measurement of the Mean Particle Diameter of Metal Fine-Particles]

In the measurement of the mean particle diameter of metalfine-particles, a microtome was (made by Leica Corporation, Ultra-CutUTC Ultra-Microtome) used to make a ultra-thin slice from a crosssection of a sample, and a transmission electron microscope (TEM;JEM-2000EX made by JEOL Ltd.) was used to observe the slice. Moreover,because a sample made on a glass substrate is difficult to observe withthe above method, another sample made on the polyimide film under thesame condition is used for the observation. Moreover, the mean particlediameter of the metal fine-particles is set to be an area mean diameter.

[Measurement of Diameter of Exposed Surfaces of Metal Fine-Particles]

The measurement of the diameter of the exposed surfaces of the metalfine-particles was conducted by observing the surface of the sampleusing a field-emission scanning electron microscope (FE-SEM from HitachiHigh-Technologies Corporation).

[Measurement of the Absorption Spectrum of the Sample]

The absorption spectra of the fabricated samples were observed withUV-visible-near IR spectroscopy, using U-4000 manufactured by Hitachi,Ltd.

[Measurement of Light Transparency]

The light transparency was measured with UV-visible spectro-analysis,using UV-vis V-550 manufactured by JASCO Corporation.

(Method for Evaluating Variations of the Peak Wavelength and PeakIntensity)

The absorption spectra of the fabricated samples respectively in theenvironments of the atmosphere, water and ethanol are observed byUV-visible-near IR spectroscopy (using U-4000 manufactured by Hitachi,Ltd.). The variation of the peak wavelength is derived as follows. Agraph was plotted, with the refractive indexes of the atmosphere, waterand ethanol (the refractive index of the atmosphere was taken as 1, thatof water taken as 1.33, and that of ethanol taken as 1.36) as thetransverse axis, and with the wavelengths at the peak tops of the peakwaveforms of the samples observed in the atmosphere, water and ethanol,respectively, as the vertical axis. The variation of the peak wavelengthper unit variation of the refractive index was then derived as the slopeof the straight line obtained with a least squares method. The variationof the peak intensity is derived as follows. A graph was plotted, withthe refractive indexes of the atmosphere, water and ethanol (therefractive index of the atmosphere was taken as 1, that of water takenas 1.33, and that of ethanol taken as 1.36) as the transverse axis, andwith the intensities at the peak tops of the peak waveforms of thesamples observed in the atmosphere, water and ethanol, respectively, asthe vertical axis. The variation of the peak intensity per unitvariation of the refractive index was then derived as the slope of thestraight line obtained with a least squares method. For obtaining a goodLSPR effect, the variation of the peak intensity per unit variation ofthe refractive index was evaluated as “good” when it was greater than orequal to 0.22 nm of Fabrication Example 2 which was taken as a standard,and was evaluated as “excellent” when it was greater than or equal to0.42 nm.

[Measurement of Water Absorption Ratio]

In the measurement of the water absorption ration, the sample was driedat 80° C. for 2 hours, and the mass a of the dried sample was measured.Then, the dried sample was placed in an environment of 23° C. and 50% RHfor 24 hours (environment test), and then the mass b of the sample wasmeasured. From such measured masses of the sample, the water absorptionratio was calculated by the following equation (A).

[Water absorption ratio (%)]={(weight b−weight a)/weight a}×100  (A)

Synthesis Example 1

In a separable flask of 500 ml, 15.24 g (47.6 mmol) of2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB) was dissolved in170 g of DMAc. Next, the solution was added with 14.76 g (47.6 mmol) of4,4′-oxydiphthalic anhydride (ODPA) under a nitrogen flow, and wasfurther stirred at room temperature for 4 hours to conduct apolymerization reaction, so that a colorless thick polyamic acid resinsolution S₁ was obtained. The viscosity of the obtained polyamic acidsolution S₁ was measured using an E-type viscometer (DV-II+Pro CP type,made by Brookfield Corporation) to be 3251 cP (25° C.). Theweight-average molecular weight (Mw) was measured with gel permeationchromatography (GPC, using HLC-8220GPC made by Tosoh Corporation) to be163,900.

The obtained polyamic acid resin solution S₁ was coated on a stainlesssubstrate, dried at 125° C. for 3 min, and then thermally treatedstepwise at 160° C. for 2 min, at 190° C. for 30 min, at 200° C. for 30min, at 220° C. for 3 min and then at 280° C., 320° C. and 360° C.respectively for 1 min to finish the imidization, so that a polyimidefilm laminated on a stainless substrate is obtained. The polyimide filmwas peeled from the stainless substrate to obtain a polyimide film P₁ of10 μm thick. The transmittance of this film under 400 nm was 95%, andthe mean transmittance of visible light was 96%.

Fabrication Example 1

A test plate of 10 cm×10 cm (0.7 mm thick) made of an alkali-free glass(AN-100 produced by Asahi Glass Co., Ltd.), was treated with a 5 Naqueous solution of sodium hydroxide of 50° C. for 5 min. Next, theglass substrate of the test plate is cleaned by pure water, dried, andthen immersed in a 1 wt % aqueous solution of3-aminopropyltrimethoxysilane (abbreviated to “γ-APS” hereafter). Theglass substrate was dried after being taken out from the aqueous γ-APSsolution, and then heated at 150° C. for 5 min to fabricate a glasssubstrate G1.

Fabrication Example 2

A test plate of 10 cm×10 cm (0.7 mm thick) made of an alkali-free glass(AN-100 produced by Asahi Glass Co., Ltd.) was surface-treated withvacuum evaporation at a pressure of 1×10⁵ Pa or lower to form a metalgold film of about 5 nm thick on the glass substrate. The substrate isthermally treated at 500° C. for 1 hour to convert the metal gold filmon the glass substrate into metal gold fine-particles, so that a testplate with metal gold fine-particles adhering to a glass substrate in adispersion state was made. The characteristics of the metal goldfine-particles on the test plate are as follows.

The shape was a semi-spherical shape, the mean particle diameter wasabout 32 nm, the minimal particle diameter was about 9.5 nm, the maximalparticle diameter was about 61 nm, the mean value of the inter-particledistances was about 13 nm, and the area fraction of the total goldfine-particles relative to the surface area of the test plate was about19%.

Moreover, the absorption spectrum of the LSPR of the test plate wasobserved to have an absorption peak with a peak top at 559 nm and ahalf-height width of 75 nm. The peak wavelength variation and the peakintensity variation per unit variation of the refractive index of theobserved absorption peak were 52 nm and 0.22, respectively.

Fabrication Example 3

3 mg of a powder reagent of Biotin N-succinimide (Biotin Sulfo-OSu,produced by Dojindo Molecular Technologies, Inc.) was dissolved in 3 mlof a phosphoric acid-buffered saline as a mixed aqueous solution of 150mM of sodium chloride, 7.5 mM of disodium hydrogenphosphate, and 2.9 mMof sodium dihydrogenphosphate, so that a Biotin solution 3 of 1 mg/mlwas prepared.

Fabrication Example 4

1 mg of a powder reagent of Avidin (Avidin from egg white, produced byNacalai Tesque, Inc.) was dissolved in 10 ml of a phosphoricacid-buffered saline as a mixed aqueous solution of 150 mM of sodiumchloride, 7.5 mM of disodium hydrogenphosphate, and 2.9 mM of sodiumdihydrogenphosphate, so that an Avidin solution 4 of 1.47 μM wasprepared.

Example 1 Fabrication of a Nano-Composite Film in which the First MetalFine-Particles were Dispersed

0.174 g of chloroauric acid tetrahydrate dissolved in 17.33 g of DMAcwas added to 2.67 g of the polyamic acid resin solution S₁ obtained inSynthesis Example, and the mixture was stirred in a nitrogen atmospherefor 15 min at room temperature to prepare a polyamic acid resin solutioncontaining a gold complex. The obtained polyamic acid resin solutioncontaining a gold complex was coated on the glass substrate G1 ofFabrication Example 1 using a spin coater (Spincoater 1H-DX2, made byMikasa Co., Ltd.), and was then dried at 70° C. for 3 min and at 130° C.for 20 min to form on the glass substrate G1 a polyamic acid resin filmof 50 nm thick that contained a gold complex. The polyamic acid resinfilm containing a gold complex was thermally treated at 300° C. for 10min, so that a nano-composite film 1 a (30 nm thick) in which metal goldfine-particles showing a red color were dispersed was fabricated. Thefirst metal gold fine-particles formed in the nano-composite film 1 awere dispersed entirely independent from each other in the regions fromthe surface layer portion of the film along the thickness direction,with a distance greater than or equal to the particle diameter of thelarger one of neighboring metal gold fine-particles. Moreover, thecharacteristics of the first metal gold fine-particles formed in thefilm are as follows.

The shape was a substantially spherical shape, the mean particlediameter was about 4.2 nm, the minimal particle diameter was about 3.0nm, the maximal particle diameter was about 9.8 nm, the volume fractionrelative to the nano-composite film 1 a was about 1.35%, and the meanvalue of the inter-particle distances was about 17.4 nm.

Moreover, the absorption spectrum of the LSPR of the first metal goldfine-particles of the nano-composite film 1 a was observed to have anabsorption peak with a peak top at 544 nm and a half-height width of 78nm.

<Step of Etching the Nano-Composite>

A vacuum plasma apparatus (Plasma Cleaner VE-1500II, manufactures byMori Engineering Co., Ltd.) was used to remove a region of 7 nm thick ofthe nano-composite film 1 a from the surface side thereof, so that anano-composite film 1 b was obtained. A part of the first metal goldfine-particles were exposed at the surface of the film at the surfaceside, and were identified to have a mean value of 3.8 nm for thediameters of the exposed surfaces of the metal gold fine-particles. Atthis moment, the area fraction of the total exposed portions of thefirst metal gold fine-particles relative to the surface area of thenano-composite film 1 b was 1.08%. Moreover, the absorption spectrum ofthe LSPR of the first metal gold fine-particles of the nano-compositefilm 1 b was observed to have an absorption peak with a peak top at 525nm and a half-height width of 68 nm. The peak wavelength variation andthe peak intensity variation per unit variation of the refractive indexof the observed absorption peak were 10.3 nm and 0.02, respectively.Moreover, the surface observation image of the nano-composite 1 b isshown in FIG. 5.

<Step of Immobilizing Binding Species>

Next, the nano-composite film 1 b was immersed in a 0.1 mM (0.1 mmol/L)ethanol solution of the hydrochloric salt of aminoundecanethiol as abinding species and treated at −6° C. for 2 hours, and was then cleanedusing ethanol. Then, the nano-composite 1 b was immersed in a 100 mMaqueous solution of potassium hydroxide and treated at 23° C. for 30sec, and was then cleaned by pure water and dried. Thereby, the ammoniumgroup of the hydrochloric salt of aminoundecanethiol was converted to anamino group, and a nano-composite film 1 c was prepared.

<Step of Immobilizing Second Metal Fine-Particles Via Binding Species>

The nano-composite film 1 c obtained as above was immersed in a metalgold colloidal solution 1 (produced by Tanaka Kikinzoku Inc., with ametal gold content of 0.007 wt %, a mean particle diameter of the metalgold colloidal particles of about 80 nm, a maximal particle diameter of141.8 nm, and a minimal particle diameter of 50.8 nm) and treated understirring at 23° C. for 2 hours, and was then cleaned by pure water anddried. Thereby, second metal gold fine-particles formed from the metalgold colloidal particles are immobilized on the first metal goldfine-particles of the nano-composite film 1 c, so that a nano-compositefilm 1 d was obtained. As shown in FIG. 6, the second metal goldfine-particles of the nano-composite film 1 d do not overlap with eachother, and are in a state of being dispersed substantially uniformly ina plane. Dispersion unevenness was not identified. Moreover, theabsorption spectrum of the LSPR of the second metal gold fine-particlesof the nano-composite film 1 d was observed to have an absorption peakwith a peak top at 514 nm and a half-height width of 57 nm. The peakwavelength variation and the peak intensity variation per unit variationof the refractive index of the observed absorption peak were 63.8 nm and0.42, respectively.

Example 2

A nano-composite film 2 d was obtained as in Example 1 except that themetal gold colloidal solution 1 used in Example 1 was replaced by ametal gold colloidal solution 2 (produced by Tanaka Kikinzoku Inc., witha metal gold content of 0.007 wt %, a mean particle diameter of themetal gold colloidal particles of about 50 nm, a maximal particlediameter of 91.3 nm, and a minimal particle diameter of 32.6 nm). Thesecond metal gold fine-particles of the nano-composite film 2 d do notoverlap with each other, and are in a state of being dispersedsubstantially uniformly in a plane. Dispersion unevenness was notidentified. Moreover, the absorption spectrum of the LSPR of the secondmetal gold fine-particles of the nano-composite film 2 d was observed tohave an absorption peak with a peak top at 514 nm and a half-heightwidth of 57 nm. The peak wavelength variation and the peak intensityvariation per unit variation of the refractive index of the observedabsorption peak were 49.4 nm and 0.33, respectively.

Example 3

A nano-composite film 3 d was obtained as in Example 1 except that thestep of using the metal gold colloidal solution 1 to treat understirring at 23° C. for 2 hours in Example 1 was replaced by a step ofusing a metal gold colloidal solution 3 (produced by Tanaka KikinzokuInc., with a metal gold content of 0.007 wt %, a mean particle diameterof the metal gold colloidal particles of about 100 nm, a maximalparticle diameter of 164.2 nm, and a minimal particle diameter of 68.1nm) to treat under stirring at 23° C. for 24 hours. The second metalgold fine-particles of the nano-composite film 3 d do not overlap witheach other, and are in a state of being dispersed substantiallyuniformly in a plane. Dispersion unevenness was not identified.Moreover, the absorption spectrum of the LSPR of the second metal goldfine-particles of the nano-composite film 3 d was observed to have anabsorption peak with a peak top at 513 nm and a half-height width of 58nm. The peak wavelength variation and the peak intensity variation perunit variation of the refractive index of the observed absorption peakwere 52.3 nm and 0.61, respectively.

Example 4

A nano-composite film 4 d was obtained as in Example 1 except that thestep of using the metal gold colloidal solution 1 to treat understirring at 23° C. for 2 hours in Example 1 was replaced by a step ofusing a metal gold colloidal solution 4 (produced by Tanaka KikinzokuInc., with a metal gold content of 0.007 wt %, a mean particle diameterof the metal gold colloidal particles of about 150 nm, a maximalparticle diameter of 220.2 nm, and a minimal particle diameter of 105.7nm) to treat under stirring at 23° C. for 24 hours. The second metalgold fine-particles of the nano-composite film 4 d do not overlap witheach other, and are in a state of being dispersed substantiallyuniformly in a plane. Dispersion unevenness was not identified.Moreover, the absorption spectrum of the LSPR of the second metal goldfine-particles of the nano-composite film 4 d was observed to have anabsorption peak with a peak top at 515 nm and a half-height width of 58nm. The peak wavelength variation and the peak intensity variation perunit variation of the refractive index of the observed absorption peakwere 69.5 nm and 0.75, respectively.

Example 5 Fabrication of Nano-Composite Film in which First MetalFine-Particles are Dispersed

A nano-composite film 5 a of 30 nm thick, in which metal goldfine-particles were dispersed, was fabricated as in Example 1 exceptthat the use of 0.174 g of chloroauric acid tetrahydrate dissolved in17.33 g of DMAc was replaced by the use of 0.087 g of chloroauric acidtetrahydrate dissolved in 17.33 g of DMAc. The first metal goldfine-particles formed in the nano-composite film 5 a were dispersedentirely independently from each other in the regions from the surfacelayer portion of the film along the thickness direction, with a distancegreater than or equal to the particle diameter of the larger one ofneighboring metal gold fine-particles. Moreover, the characteristics ofthe first metal gold fine-particles formed in the film are as follows.

The shape was a substantially spherical shape, the mean particlediameter was about 3.8 nm, the minimal particle diameter was about 2.8nm, the maximal particle diameter was about 9.5 nm, the volume fractionrelative to the nano-composite film 5 a was about 0.682%, and the meanvalue of the inter-particle distances was about 12.4 nm.

Moreover, the absorption spectrum of the LSPR of the first metal goldfine-particles of the nano-composite film 5 a was observed to have anabsorption peak with a peak top at 544 nm and a half-height width of 76nm.

<Step of Etching the Nano-Composite>

A nano-composite film 5 b was obtained by conducting etching in the sameway of Example 1. On the surface at the surface side of the film, a partof the first metal gold fine-particles were exposed, and the averageddiameter of the exposed surfaces of the metal gold fine-particles wasidentified to be about 3.5 nm. At this moment, the area fraction of thetotal exposed portions of the first metal gold fine-particles relativeto the surface area of the nano-composite film 5 b was 0.50%. Moreover,the absorption spectrum of the LSPR of the first metal goldfine-particles of the nano-composite film 5 b was observed to have anabsorption peak with a peak top at 534 nm and a half-height width of 68nm. The peak wavelength variation and the peak intensity variation perunit variation of the refractive index of the observed absorption peakwere 7.5 nm and 0.001, respectively.

<Step of Immobilizing Binding Species>

A nano-composite film 5 c was prepared by immobilizing the bindingspecies in the same way of Example 1.

<Step of Immobilizing Second Metal Fine-Particles Via Binding Species>

In the same way of Example 1, the nano-composite film 5 c was immersedin the metal gold colloidal solution 1 to obtain a nano-composite film 5d. The second metal gold fine-particles of the nano-composite film 5 ddo not overlap with each other, and are in a state of being dispersedsubstantially uniformly in a plane. Dispersion unevenness was notidentified. Moreover, the absorption spectrum of the LSPR of the secondmetal gold fine-particles of the nano-composite film 5 d was observed tohave an absorption peak with a peak top at 512 nm and a half-heightwidth of 57 nm. The peak wavelength variation and the peak intensityvariation per unit variation of the refractive index of the observedabsorption peak were 73.7 nm and 0.31, respectively.

Example 6

A nano-composite film 6 d was obtained as in Example 5 except that thestep of using the metal gold colloidal solution 1 to treat understirring at 23° C. for 2 hours in Example 5 was replaced by a step ofusing the metal gold colloidal solution 3 (produced by Tanaka KikinzokuInc., with a metal gold content of 0.007 wt % and a mean particlediameter of the metal gold colloidal particles of about 100 nm) to treatunder stirring at 23° C. for 24 hours. The second metal goldfine-particles of the nano-composite film 6 d do not overlap with eachother, and are in a state of being dispersed substantially uniformly ina plane. Dispersion unevenness was not identified. Moreover, theabsorption spectrum of the LSPR of the second metal gold fine-particlesof the nano-composite film 6 d was observed to have an absorption peakwith a peak top at 514 nm and a half-height width of 57 nm. The peakwavelength variation and the peak intensity variation per unit variationof the refractive index of the observed absorption peak were 66.7 nm and0.48, respectively.

Example 7

A nano-composite film 7 d was obtained as in Example 5 except that thestep of using the metal gold colloidal solution 1 to treat understirring at 23° C. for 2 hours in Example 5 was replaced by a step ofusing the metal gold colloidal solution 4 (produced by Tanaka KikinzokuInc., with a metal gold content of 0.007 wt % and a mean particlediameter of the metal gold colloidal particles of about 150 nm) to treatunder stirring at 23° C. for 24 hours. The second metal goldfine-particles of the nano-composite film 7 d do not overlap with eachother, and are in a state of being dispersed substantially uniformly ina plane. Dispersion unevenness was not identified. Moreover, theabsorption spectrum of the LSPR of the second metal gold fine-particlesof the nano-composite film 7 d was observed to have an absorption peakwith a peak top at 522 nm and a half-height width of 60 nm. The peakwavelength variation and the peak intensity variation per unit variationof the refractive index of the observed absorption peak were 55.5 nm and0.38, respectively.

Example 8

<Fabrication of Nano-Composite Film in which First Metal Fine-Particlesare Dispersed>

A nano-composite film 8 a of 30 nm thick, in which metal goldfine-particles were dispersed, was fabricated as in Example 1 exceptthat the use of 0.174 g of chloroauric acid tetrahydrate dissolved in17.33 g of DMAc was replaced by the use of 0.058 g of chloroauric acidtetrahydrate dissolved in 17.33 g of DMAc. The first metal goldfine-particles formed in the nano-composite film 8 a were dispersedentirely independently from each other in the regions from the surfacelayer portion of the film along the thickness direction, with a distancegreater than or equal to the particle diameter of the larger one ofneighboring metal gold fine-particles. Moreover, the characteristics ofthe first metal gold fine-particles formed in the film are as follows.

The shape was a substantially spherical shape, the mean particlediameter was about 3.7 nm, the minimal particle diameter was about 2.8nm, the maximal particle diameter was about 9.1 nm, the volume fractionrelative to the nano-composite film 8 a was about 0.456%, and the meanvalue of the inter-particle distances was about 14.3 nm.

Moreover, the absorption spectrum of the LSPR of the first metal goldfine-particles of the nano-composite film 8 a was observed to have anabsorption peak with a peak top at 543 nm and a half-height width of 79nm.

<Step of Etching the Nano-Composite>

A nano-composite film 8 b was obtained by conducting etching in the sameway of Example 1. On the surface at the surface side of the film, a partof the first metal gold fine-particles were exposed, and the averageddiameter of the exposed surfaces of the metal gold fine-particles wasidentified to be about 3.5 nm. At this moment, the area fraction of thetotal exposed portions of the first metal gold fine-particles relativeto the surface area of the nano-composite film 8 b was 0.42%. Moreover,from the absorption spectrum of the LSPR of the first metal goldfine-particles of the nano-composite film 8 b, a peak top and ahalf-height width were difficult to measure.

<Step of Immobilizing Binding Species>

A nano-composite film 8 c was prepared by immobilizing the bindingspecies in the same way of Example 1.

<Step of Immobilizing Second Metal Gold Fine-Particles Via BindingSpecies>

In the same way of Example 1, the nano-composite film 8 c was immersedin the metal gold colloidal solution 1 to obtain a nano-composite film 8d. The second metal gold fine-particles of the nano-composite film 8 ddo not overlap with each other, and are in a state of being dispersedsubstantially uniformly in a plane. Dispersion unevenness was notidentified. Moreover, the absorption spectrum of the LSPR of the secondmetal gold fine-particles of the nano-composite film 8 d was observed tohave an absorption peak with a peak top at 514 nm and a half-heightwidth of 58 nm. The peak wavelength variation and the peak intensityvariation per unit variation of the refractive index of the observedabsorption peak were 65.4 nm and 0.35, respectively.

Example 9

A nano-composite film 9 d was obtained as in Example 8 except that theuse of the metal gold colloidal solution 1 in Example 8 was replaced bythe use of the metal gold colloidal solution 2 (produced by TanakaKikinzoku Inc., with a metal gold content of 0.007 wt % and a meanparticle diameter of the metal gold colloidal particles of about 50 nm).The second metal gold fine-particles of the nano-composite film 9 d donot overlap with each other, and are in a state of being dispersedsubstantially uniformly in a plane. Dispersion unevenness was notidentified. Moreover, the absorption spectrum of the LSPR of the secondmetal gold fine-particles of the nano-composite film 9 d was observed tohave an absorption peak with a peak top at 514 nm and a half-heightwidth of 57 nm. The peak wavelength variation and the peak intensityvariation per unit variation of the refractive index of the observedabsorption peak were 56.4 nm and 0.15, respectively.

Example 10

A nano-composite film 10 d was obtained as in Example 8 except that thestep of using the metal gold colloidal solution 1 to treat understirring at 23° C. for 2 hours in Example 8 was replaced by a step ofusing the metal gold colloidal solution 3 (produced by Tanaka KikinzokuInc., with a metal gold content of 0.007 wt % and a mean particlediameter of the metal gold colloidal particles of about 100 nm) to treatunder stirring at 23° C. for 24 hours. The second metal goldfine-particles of the nano-composite film 10 d do not overlap with eachother, and are in a state of being dispersed substantially uniformly ina plane. Dispersion unevenness was either not identified. Moreover, theabsorption spectrum of the LSPR of the second metal gold fine-particlesof the nano-composite film 10 d was observed to have an absorption peakwith a peak top at 514 nm and a half-height width of 59 nm. The peakwavelength variation and the peak intensity variation per unit variationof the refractive index of the observed absorption peak were 66.7 nm and0.49, respectively.

Example 11 Fabrication of Nano-Composite Film in which First MetalFine-Particles are Dispersed

A nano-composite film 11 a of 30 nm thick, in which metal goldfine-particles were dispersed, was fabricated as in Example 1 exceptthat the use of 0.174 g of chloroauric acid tetrahydrate dissolved in17.33 g of DMAc was replaced by the use of 0.522 g of chloroauric acidtetrahydrate dissolved in 17.33 g of DMAc. The first metal goldfine-particles formed in the nano-composite film 11 a were dispersedentirely independently from each other in the regions from the surfacelayer portion of the film along the thickness direction, with a distancegreater than or equal to the particle diameter of the larger one ofneighboring metal gold fine-particles, and with a side-by-sidearrangement in a single layer. Moreover, the characteristics of thefirst metal gold fine-particles formed in the film are as follows.

The shape was a substantially spherical shape, the mean particlediameter was about 20 nm, the minimal particle diameter was about 12 nm,the maximal particle diameter was about 26 nm, the volume fractionrelative to the nano-composite film 11 a was about 3.96%, and the meanvalue of the inter-particle distances was about 25 nm.

Moreover, the absorption spectrum of the LSPR of the first metal goldfine-particles of the nano-composite film 11 a was observed to have anabsorption peak with a peak top at 546 nm and a half-height width of 102nm.

<Step of Etching the Nano-Composite>

A nano-composite film 1 b was obtained by conducting etching in the sameway of Example 1. On the surface at the surface side of the film, a partof the first metal gold fine-particles were exposed, and the averageddiameter of the exposed surfaces of the metal gold fine-particles wasidentified to be about 17.9 nm. At this moment, the area fraction of thetotal exposed portions of the first metal gold fine-particles relativeto the surface area of the nano-composite film 11 b was 3.2%. Moreover,the absorption spectrum of the LSPR of the second metal goldfine-particles of the nano-composite film 11 b was observed to have anabsorption peak with a peak top at 528 nm and a half-height width of 80nm. The peak wavelength variation and the peak intensity variation perunit variation of the refractive index of the observed absorption peakwere −5.8 nm and 0.02, respectively.

<Step of Immobilizing Binding Species>

A nano-composite film 11 c was prepared by immobilizing the bindingspecies in the same way of Example 1.

<Step of Immobilizing Second Metal Gold Fine-Particles Via BindingSpecies>

In the same way of Example 1, the nano-composite film 11 c was immersedin the metal gold colloidal solution 1 to obtain a nano-composite film11 d. The second metal gold fine-particles of the nano-composite film 1d do not overlap with each other, and are in a state of being dispersedsubstantially uniformly in a plane. Dispersion unevenness was notidentified. Moreover, the absorption spectrum of the LSPR of the secondmetal gold fine-particles of the nano-composite film 11 d was observedto have an absorption peak with a peak top at 524 nm and a half-heightwidth of 72 nm. The peak wavelength variation and the peak intensityvariation per unit variation of the refractive index of the observedabsorption peak were 56.4 nm and 0.24, respectively.

Example 12

A nano-composite film 12 d was obtained as in Example 11 except that thestep of using the metal gold colloidal solution 1 to treat understirring at 23° C. for 2 hours in Example 11 was replaced by a step ofusing the metal gold colloidal solution 3 (produced by Tanaka KikinzokuInc., with a metal gold content of 0.007 wt % and a mean particlediameter of the metal gold colloidal particles of about 100 nm) to treatunder stirring at 23° C. for 24 hours. The second metal goldfine-particles of the nano-composite film 12 d do not overlap with eachother, and are in a state of being dispersed substantially uniformly ina plane. Dispersion unevenness was not identified. Moreover, theabsorption spectrum of the LSPR of the second metal gold fine-particlesof the nano-composite film 12 d was observed to have an absorption peakwith a peak top at 514 nm and a half-height width of 58 nm. The peakwavelength variation and the peak intensity variation per unit variationof the refractive index of the observed absorption peak were 56.4 nm and0.63, respectively.

Example 13

A nano-composite film 13 d was obtained as in Example 11 except that thestep of using the metal gold colloidal solution 1 to treat understirring at 23° C. for 2 hours in Example 11 was replaced by a step ofusing the metal gold colloidal solution 4 (produced by Tanaka KikinzokuInc., with a metal gold content of 0.007 wt % and a mean particlediameter of the metal gold colloidal particles of about 150 nm) to treatunder stirring at 23° C. for 24 hours. The second metal goldfine-particles of the nano-composite film 13 d do not overlap with eachother, and are in a state of being dispersed substantially uniformly ina plane. Dispersion unevenness was not identified. Moreover, theabsorption spectrum of the LSPR of the second metal gold fine-particlesof the nano-composite film 13 d was observed to have an absorption peakwith a peak top at 526 nm and a half-height width of 60 nm. The peakwavelength variation and the peak intensity variation per unit variationof the refractive index of the observed absorption peak were 51.9 nm and0.25, respectively.

Example 14

A nano-composite film 14 d with immobilized second metal goldfine-particles was obtained in the same way of Example 1.

Next, the nano-composite film 14 d was immersed in a 0.1 mM (0.1 mmol/L)ethanol solution of the hydrochloric salt of aminoundecanethiol as abinding species and treat at 23° C. for 2 hours, and was then cleanedwith ethanol and dried to prepare a nano-composite film 14 e.

Next, the nano-composite film 14 e was immersed in the Biotin solution 3of Fabrication Example 3 and treat at 23° C. for 2 hours, and was thencleaned with a phosphoric acid-buffered saline and then immersed in thephosphoric acid-buffered saline. Thereby, a nano-composite film 14 e′was prepared with Biotin N-succinimidyl further immobilized on thebinding species of the nano-composite film 14 e. The absorption spectrumof the nano-composite film 14 e′ in the phosphoric acid-buffered salinewas observed to have an absorption peak with a peak top at 535 nm, ahalf-height width of 58 nm, and a peak top absorbance of 0.250.

The nano-composite film 14 e′ was immersed in the Avidin solution 4 ofFabrication Example 4 and treat under stirring at 23° C. for 2 hours,and was then cleaned with a phosphoric acid-buffered saline and thenimmersed in the phosphoric acid-buffered saline. Thereby, anano-composite film 14 e″ was prepared with Avidin adsorbed by theBiotin moiety of the binding species of the nano-composite film 14 e′.The absorption spectrum of the nano-composite film 14 e″ in thephosphoric acid-buffered saline was observed to have an absorption peakwith a peak top at 539 nm, a half-height width of 58 nm, and a peak topabsorbance of 0.278.

Reference Example 1

17.33 g of DMAc was added in 2.67 g of the polyamic acid resin solutionS₁ obtained in Synthesis Example 1 to dilute the polyamic acid resinsolution S₁. The resulting polyamic acid resin solution was coated on aglass substrate G1 of Fabrication Example 1 using a spin coater(Spincoater 1H-DX2, made by Mikasa Co., Ltd.), and was then dried at 70°C. for 3 min and 130° C. for 20 min, so that a polyamic acid resin filmof 50 nm thick was formed on the glass substrate G1. By thermallytreating the polyamic acid resin film at 300° C. for 10 min, a colorlesstransparent polyimide film of 30 nm thick was fabricated.

<Step of Immobilizing Binding Species>

Next, the polyimide film was immersed in a 0.1 mM (0.1 mmol/L) ethanolsolution of the hydrochloric salt of aminoundecanethiol as a bindingspecies and treated at 23° C. for 2 hours, and was then cleaned withethanol and dried to prepare a polyimide film with an immobilizedbinding species.

<Step of Immobilizing Metal Colloidal Particles Via Binding Species>

The polyimide film obtained as above was immersed in the metal goldcolloidal solution 1 (produced by Tanaka Kikinzoku Inc., with a metalgold content of 0.007 wt % and a mean particle diameter of the metalgold colloidal particles of about 80 nm) and treated under stirring at23° C. for 2 hours, and was then cleaned by pure water and dried. Theresulting polyimide film was found to have metal gold colloidalparticles adhering to its surface in an aggregation state, as shown inFIG. 7. The absorption spectrum thereof was observed to have a broadabsorption peak in the wavelength region of 600 nm to 800 nm, which wascaused by the aggregated metal gold colloidal particles.

Reference Example 2

In the same way of Example 1, a nano-composite film in which metal goldfine-particles were dispersed was obtained, and a nano-composite filmhaving been subjected to an etching step was fabricated.

<Step of Immobilizing Binding Species>

The nano-composite film obtained as above was immersed in a 0.1 mM (0.1mmol/L) ethanol solution of the hydrochloric salt of aminoundecanethiolas a binding species and treated at 23° C. for 2 hours, and was thencleaned with ethanol and dried. Next, the nano-composite film wasimmersed in a 100 mM aqueous solution of potassium hydroxide and treatedat 23° C. for 30 min, and was then cleaned with pure water and dried.Thereby, the ammonium group in the hydrochloric salt ofaminoundecanethiol was converted to an amino group, and the bindingspecies is immobilized all over the entire surface of the nano-compositefilm.

<Step of Immobilizing Metal Colloidal Particles Via Binding Species>

The nano-composite film obtained as above was immersed in the metal goldcolloidal solution 1 (produced by Tanaka Kikinzoku Inc., with a metalgold content of 0.007 wt % and a mean particle diameter of the metalgold colloidal particles of about 80 nm) and treated under stirring at23° C. for 2 hours, and was then cleaned by pure water and dried. Theresulting nano-composite film was found to have metal gold colloidalparticles adhering to its surface in an aggregation state, as shown inFIG. 8. The absorption spectrum thereof was observed to have a broadabsorption peak in the wavelength region of 600 nm to 800 nm that wascaused by the aggregated metal gold colloidal particles.

It is clear from the above results that the nano-composite filmsobtained in Examples 1-14 exhibited a sufficient intensity of theabsorption spectrum of the LSPR of the second metal gold fine-particlesformed from metal gold colloidal particles, and a sharp absorption peakwith a small half-height width. Therefore, it was confirmed that thenano-composite films allow a high-sensitivity detection when being usedin certain applications, such as bio-sensors, etc.

Though this invention has been described with the above embodiments, theinvention is not limited as such, and various modifications are allowed.This international application claims the priority benefits of JapanesePatent Application No. 2010-123225 filed on May 28, 2010, of which theentire contents are cited.

What is claimed is:
 1. A metal fine-particle composite, comprising: a matrix resin, and metal fine-particles immobilized to the matrix resin, wherein a) the metal fine-particles include a plurality of first metal fine-particles immobilized in the matrix resin, and second metal fine-particles indirectly immobilized on the first metal fine-particles, b) the first metal fine-particles are present independently without contacting with each other, and c) each of at least a part of the first metal fine-particles has a portion embedded in the matrix resin and another portion exposed outside of the matrix resin, while the second metal fine-particles are immobilized via a binding species immobilized on the another exposed portion.
 2. The metal fine-particle composite of claim 1, wherein the first metal fine-particles have particle diameters in a range of 1 nm to 50 nm and a mean particle diameter greater than or equal to 3 nm, and the second metal fine-particles have a mean particle diameter in a range of 40 nm to 200 nm.
 3. The metal fine-particle composite of claim 1, wherein the first metal fine-particles are present with a distance that is greater than or equal to a particle diameter of a larger one of two neighboring fine-particles among the first metal fine-particles.
 4. The metal fine-particle composite of claim 1, wherein another binding species having a functional group interacting with a specific substance is immobilized on surfaces of the second metal fine-particles.
 5. The metal fine-particle composite of claim 1, wherein the second metal fine-particles are formed from a metal colloidal.
 6. A method for producing the metal fine-particle composite of claim 1, the method comprising: A) a step of contacting the first metal fine-particles, each of which has a portion embedded in the matrix resin and another portion exposed outside of the matrix resin, with a treating liquid containing the binding species at a temperature of 20° C. or lower to selectively binding the binding species to the another exposed portion; and B) a step of immobilizing the second metal fine-particles via the immobilized binding species.
 7. The method of claim 6, further comprising, before the step A, C) a step of forming a resin film containing a metal ion or a metal salt; D) a step of thermally reducing the metal ion or the metal salt in the resin film to separate out the plurality of first metal fine-particles in the matrix resin and E) a step of etching a surface of the matrix resin to partially expose a surface of each of at least the part of the first metal fine-particles.
 8. The method of claim 6, further comprising, after the step B, F) a step of immobilizing, on surfaces of the second metal fine-particles, another binding species having a functional group interacting with a specific substance.
 9. The method of claim 6, wherein the step B uses a metal colloidal solution containing the second metal fine-particles in a form of metal colloidal. 